Boosting Energy Efficiency and Stability of Li-CO2 Batteries via Synergy between Ru Atom Clusters and Single-Atom Ru-N4 sites in the Electrocatalyst Cathode

High-Performance Aprotic Li-CO2 Battery Enabled by the Ru Heterophase Catalyst

Aprotic Li-CO2 batteries (LCBs) hold promise for mitigating the greenhouse effect while generating electric power, yet their development remains nascent due to the sluggish CO2 activation and irreversible discharge product formation, requiring efficient catalysts to address these challenges. Herein, we developed ∼5.5 nm fcc + hcp Ru heterophase nanoparticles on a Ketjen black (KB) matrix (Rufcc+hcp/KB) as a dual-functional catalyst for LCBs. X-ray absorption spectroscopy revealed charge redistribution in the fcc + hcp heterophase and under-coordinated Ru sites, which serve as abundant active sites to boost catalytic activity. Theoretical calculations evidenced that the heterophase interface lowers the free energy barriers of the desorption of the *Li2CO3 step (*Li2CO3 → Li2CO3) and the decomposition of the *Li2C2O4 step (*Li2C2O4 → *LiC2O4 + Li), facilitating both the nucleation and decomposition of Li2CO3. Thus, the Rufcc+hcp/KB catalyst exhibited a low overpotential of 0.73 V and long-term cycling stability exceeding 2260 h (at 100 mA g-1 with a capacity of 1000 mA h g-1), outperforming Rufcc/KB (1.14 V, 1260 h), Ruhcp/KB (0.90 V, 1480 h), and previously reported Ru-based catalysts. Our findings highlight crystalline phase engineering as an effective strategy to enhance catalytic performance in LCBs.

Synergistic Ru Species on Poly(heptazine imide) Enabling Efficient Photocatalytic CO2 Reduction with H2O beyond 800 nm

Photocatalytic CO2 conversion with H2O to carbonaceous fuels is a desirable strategy for CO2 management and solar utilization, yet its efficiency remains suboptimal. Herein, efficient and durable CO2 photoreduction is realized over a RuNPs/Ru-PHI catalyst assembled by anchoring Ru single atoms (SAs) and nanoparticles (NPs) onto poly(heptazine imide) (PHI) via the in-plane Ru-N4 coordination and interfacial Ru-N bonds, respectively. This catalyst shows an unsurpassed CO production (32.8 µmol h-1), a record-high apparent quantum efficiency (0.26%) beyond 800 nm, and the formation of the valuable H2O2. Ru SAs tune PHI's electronic structure to promote in-plane charge transfer to Ru NPs, forming a built-in electron field at the interface, which directs electron-hole separation and rushes excited electron movement from Ru-PHI to Ru NPs. Simultaneously, Ru SAs introduce an impurity level in PHI to endow long-wavelength photoabsorption, while Ru NPs strengthen CO2 adsorption/activation and expedite CO desorption. These effects of Ru species together effectively ensure CO2-to-CO conversion. The CO2 reduction on the catalyst is revealed to follow the pathway CO2→ *CO2→ *COOH→ *CO→ CO, based on the intermediates identified by in situ diffuse reflectance infrared Fourier transform spectroscopy and further supported by density functional theory calculations.

Electron effect regulation: A study on the influence of electron-donating and withdrawing group modification on the performance of metal-coordinated catalysts for electrochemical carbon dioxide reduction

Electron effect regulation is a crucial factor influencing the activity and selectivity of Cu-based coordination compound catalysts in the electrochemical carbon dioxide reduction reaction (CO2RR). Despite significant progress, the structure-activity relationship and the underlying regulatory mechanisms warrant further in-depth investigation. In this study, three types of Cu-[ONNO] tetradentate coordination molecular catalysts with varying electron densities, namely Cu-N2O2, methoxy-modified Cu-N2O2 (Cu-EDG-N2O2), and nitro-modified Cu-N2O2 (Cu-EWG-N2O2), were prepared using a substituent regulation strategy. The prepared catalyst's micromorphology and structural characteristics were analyzed using various characterization methods. Systematic electrocatalytic CO2RR experiments were conducted to evaluate the performance of these catalysts. Compared to the unmodified Cu-N2O2, the Cu-EDG-N2O2 catalyst exhibited superior reduction performance for CH4 and C2H4 products. At an applied potential of -1.7 V vs. the reversible hydrogen electrode, the Faradaic efficiencies for CH4 and C2H4 of Cu-EDG-N2O2 were 37.8 ± 2.2 % and 25.0 ± 0.5 %, respectively. In contrast, the Cu-EWG-N2O2 catalyst demonstrated higher activity towards the production of H2 as a by-product. The effects of electronic properties of substitutions on catalyst performance were revealed by combining experimental characterization and theoretical simulation. The results showed that the conjugation effect of the -OCH3 group facilitates faster electron transfer between Cu and CO2, thereby enhancing CO2RR activity. Additionally, the introduction of different substituents modulates the local microenvironment around the Cu active centers, significantly influencing the catalytic performance. This study provides valuable theoretical and experimental insights into the design of efficient Cu-N2O2-type metal coordination electrocatalysts for CO2RR processes.

Asymmetric Charge Distribution in Atomically Precise Metal Nanoclusters for Boosted CO2 Reduction Catalysis

Recently, atomically precise metal nanoclusters (NCs) have been widely applied in CO2 reduction reaction (CO2RR), achieving exciting activity and selectivity and revealing structure-performance correlation. However, at present, the efficiency of CO2RR is still unsatisfactory and cannot meet the requirements of practical applications. One of the main reasons is the difficulty in CO2 activation due to the chemical inertness of CO2. Constructing symmetry-breaking active sites is regarded as an effective strategy to promote CO2 activation by modulating electronic and geometric structure of CO2 molecule. In addition, in the subsequent CO2RR process, asymmetric charge distributed sites can break the charge balance in adjacent adsorbed C1 intermediates and suppress electrostatic repulsion between dipoles, benefiting for C-C coupling to generate C2+ products. Although compared to single atoms, metal nanoparticles, and inorganic materials the research on the construction of asymmetric catalytic sites in metal NCs is in a newly-developing stage, the precision, adjustability and diversity of metal NCs structure provide many possibilities to build asymmetric sites. This review summarizes several strategies of construction asymmetric charge distribution in metal NCs for boosting CO2RR, concludes the mechanism investigation paradigm of NCs-based catalysts, and proposes the challenges and opportunities of NCs catalysis.

Constructing SiO2-Supported Atomically Dispersed Platinum Catalysts with Single-Atom and Atomic Cluster Dual Sites to Tame Hydrogenation Performance

Construction and optimization of stable atomically dispersed metal sites on SiO2 surfaces are important yet challenging topics. In this work, we developed the amino group-assisted atomic layer deposition strategy to deposit the atomically dispersed Pt on SiO2 support for the first time, in which the particle size and ratio of Pt entities from single atom (Pt1) to atomic cluster (Pt n ) and nanoparticle (Pt p ) on the SiO2 surface were well modulated. We demonstrated the importance of dual-site synergy for optimizing the activity of single-atom catalysts. The Pt1+n /SiO2-N catalysts with the coexistence of Pt1 and Pt n showed excellent activity and optimized selectivity (99% for haloanilines) in halonitrobenzenes hydrogenation, while Pt1/SiO2-N catalysts were almost inactive in the reaction. Mechanism investigation indicates that the Pt n site is beneficial for H2 dissociation, and the Pt1 site is energetically favorable for adsorption of the nitro group to complete the selective hydrogenation, which synergistically contributes to the optimized catalytic performances. This study provides a new strategy for constructing atomically dispersed metal species over the SiO2 support and demonstrates the significance of the synergy of dual active sites for enhancing the catalytic efficiency.

Theory-Guided Design of Unconventional Phase Metal Heteronanostructures for Higher-Rate Stable Li-CO2 and Li-Air Batteries

Lithium-carbon dioxide (Li-CO2) and Li-air batteries hold great potential in achieving carbon neutral given their ultrahigh theoretical energy density and eco-friendly features. However, these Li-gas batteries still suffer from low discharging-charging rate and poor cycling life due to sluggish decomposition kinetics of discharge products especially Li2CO3. Here we report the theory-guided design and preparation of unconventional phase metal heteronanostructures as cathode catalysts for high-performance Li-CO2/air batteries. The assembled Li-CO2 cells with unconventional phase 4H/face-centered cubic (fcc) ruthenium-nickel heteronanostructures deliver a narrow discharge-charge gap of 0.65 V, excellent rate capability and long-term cycling stability over 200 cycles at 250 mA g-1. The constructed Li-air batteries can steadily run for above 150 cycles in ambient air. Electrochemical mechanism studies reveal that 4H/fcc Ru-Ni with high-electroactivity facets can boost redox reaction kinetics and tune discharge reactions towards Li2C2O4 path, alleviating electrolyte/catalyst failures induced by the aggressive singlet oxygen from solo decomposition of Li2CO3.

Targeted anchoring of Cu sites in imine-based covalent organic frameworks as catalytic centers for efficient Li-CO2 batteries

Lithium-carbon dioxide (Li-CO2) batteries have attracted much attention due to their high theoretical energy density and reversible CO2 reduction/evolution process. However, the wide bandgap insulating discharge product Li2CO3 is difficult to decompose, leading to large polarization or even death of the battery, thus seriously hindering the practical application of Li-CO2 batteries. The properties of covalent organic framework (COF) materials, which can support the construction of multiphase catalytic systems, have great potential in the fields of CO2 enrichment and electrocatalytic reduction. In this paper, the excellent redox properties of transition metal were utilized to introduce Cu metal into an imine-based COF to form Cu-O,N sites as the active sites for CO2 oxidation and reduction. The electrochemical performance of the Cu sites in Li-CO2 batteries was investigated, and the prepared batteries were able to cycle stably at a current density of 200 mA g-1 for more than 1100 h. COF structural sites can be anchored by metal Cu sites to form Cu-O,N active centers for CO2 oxidation and reduction processes. This study provides a new approach for the development of lithium CO2 batteries towards more stable and stable.

Enhanced Cycle Performance of Rechargeable Li-CO2 Batteries Using Nanostructured AMn2O4 (A = Ni, Zn, Co) Electrocatalysts

Rechargeable Li-CO2 batteries face challenges of sluggish reaction kinetics and poor rechargeability. Highly efficient electrocatalysts are urgently needed to decompose the discharge product, Li2CO3. Mn-based transition metal oxides are regarded as promising candidates for improving the cycle performance and reaction kinetics of Li-CO2 batteries. Notably, morphology engineering plays a vital role in enhancing electrocatalytic performance by tuning the structure of the electrode. Herein, we adopted a morphology engineering strategy to develop nanostructured Mn-based electrocatalysts with high surface area and rich active sites. The nanostructured electrocatalysts were synthesized using a facile anodic electrodeposition method by depositing Mn-based hydroxides directly onto a carbon cloth electrode, followed by a calcination process. The electrochemical characterization showed that the Li-CO2 battery with Mn-based transition metal oxides AMn2O4 (A = Ni, Zn, Co) achieves impressive cycle performance (over 150 cycles at 100 mA/g). This work not only exhibits the excellent electrocatalytic performance of Mn-based transition metal oxide but also demonstrates a general selection principle for next-generation electrocatalysts for metal-CO2 batteries.

Zn and Cl Coregulated MXene Catalyst Enhances Li-CO2 Battery Reversibility

MXenes are promising cathodes for Li-CO2 batteries owing to their high electrical conductivity and efficient CO2 activation function. However, the effects of adsorption and electronic structures of MXene on the full life cycle of Li-CO2 batteries have been rarely investigated. Here, we employ a coregulation approach to enhance the adsorption-decomposition of lithium carbonate (Li2CO3) by introducing Zn and Cl surface groups onto the Ti3C2 MXene (Zn-Ti3C2Cl2) catalyst. The incorporation of Cl surface groups enhances Li2CO3 adsorption on the MXene catalyst surface, resulting in the formation of small-sized and uniform Li2CO3. Additionally, the introduction of Zn shifts the d-band centers of titanium and promotes CO2 evolution reaction (CO2ER) activity, thereby facilitating the decomposition of discharge products. As a result, the Li-CO2 battery based on the Zn-Ti3C2Cl2 catalyst exhibits an ultralow overpotential (0.72 V) at 200 mA g-1 and stable cycling for up to 1500 h. This work validates the efficacy of promoting reversibility in Li-CO2 batteries by adjusting the adsorption-decomposition process.

Trimetallic FeNiCu Atomic Clusters Supported on Carbon Matrix: Highly Active Catalysts for C3H6-SCR of NO

C3H6-SCR denitrification technology faces catalyst deactivation problems and low catalytic performance at medium-low temperatures. This study utilized the intermetallic synergies to prepare atomic cluster catalysts (FeNiCu/NC) by anchoring Fe-Ni-Cu on a carbon matrix to enhance the C3H6-SCR performance at medium-low temperatures. The synergistic effect of the Fe-Ni-Cu is reflected in the differences in the physicochemical properties of the catalysts, which is proved by several characterization techniques. Results showed that the FeNiCu/NC catalyst had a larger surface area (541.4 m2/g) and there were no metal oxides on the surface of the catalyst but abundant defective sites that anchored Fe/Ni/Cu atoms through N atoms to form M-Nx active sites and atomic clusters. The hollow carbon morphology provides sufficient active sites for C3H6-SCR. The coordination environments of active sites were M-Nx-C, Fe2/FeCu2/FeNi2, Ni3/NiFe/NiCu2, and Cu4/CuFe2/CuNi2, where the synergistic action of trimetal leads to the presence of Fe-Ni-Cu-Nx-C. The synergistic action of the Fe-Ni-Cu significantly improved the C3H6-SCR performance at medium-low temperatures. The FeNiCu/NC exhibited an 81% NO conversion at 150 °C under 2% O2, 15% and 20% higher than FeNi/NC and FeCu/NC catalysts, respectively. Even at 4% O2, the FeNiCu/NC catalyst was active to remove 78% NO and achieve a 93% N2 selectivity at 150 °C and maintained a 100% NO conversion at 300-425 °C. The DRIFTS results demonstrated that NO and C3H6 could combine with active O at metal cluster, M-Nx, or defective oxygen sites to produce various intermediate species, wherein acetates and nitrates were the main active intermediates. Based on the DRIFTS results, a reaction pathway for C3H6-SCR over the FeNiCu/NC catalyst was proposed.

Routes to Bidirectional Cathodes for Reversible Aprotic Alkali Metal-CO2 Batteries

Aprotic alkali metal-CO2 batteries (AAMCBs) have garnered significant interest owing to fixing CO2 and providing large energy storage capacity. The practical implementation of AAMCBs is constrained by the sluggish kinetics of the CO2 reduction reaction (CO2RR) and the CO2 evolution reaction (CO2ER). Because the CO2ER and CO2RR take place on the cathode, which connects the internal catalyst with the external environment. Building a bidirectional cathode with excellent CO2ER and CO2RR kinetics by optimizing the cathode's internal catalyst and environment has attracted most of the attention to improving the electrochemical performance of AAMCBs. However, there remains a lack of comprehensive understanding. This review aims to give a route to bidirectional cathodes for reversible AAMCBs, by systematically discussing engineering strategies of both the internal catalyst (atomic, nanoscopic, and macroscopic levels) and the external environment (photo, photo-thermal, and force field). The CO2ER and CO2RR mechanisms and the "engineering strategies from internal catalyst to the external environment-cathode properties-CO2RR and CO2ER kinetics and mechanisms-batteries performance" relationship are elucidated by combining computational and experimental approaches. This review establishes a fundamental understanding for designing bidirectional cathodes and gives a route for developing reversible AAMCBs and similar metal-gas battery systems.

Efficient Holes Abstraction by Precisely Decorating Ruthenium Single Atoms and RuOx Clusters on ZnIn2S4 for Photocatalytic Pure Water Splitting

Developing efficient photocatalysts for two-electron water splitting with simultaneous H2O2 and H2 generation shows great promise for practical application. Currently, the efficiency of two-electron water splitting is still restricted by the low utilization of photogenerated charges, especially holes, of which the transfer rate is much slower than that of electrons. Herein, Ru single atoms and RuOx clusters are co-decorated on ZnIn2S4 (RuOx/Ru-ZIS) to employ as multifunctional sites for efficient photocatalytic pure water splitting. Doping of Ru single atoms in the ZIS basal plane enhances holes abstraction from bulk ZIS by regulating the electronic structure, and RuOx clusters offer a strong interfacial electric field to remarkably promote the out-of-plane migration of holes from ZIS. Moreover, Ru single atoms and RuOx clusters also serve as active sites for boosting surface water oxidation. As a result, an excellent H2 and H2O2 evolution rates of 581.9 µmol g-1 h-1 and 464.4 µmol g-1 h-1 is achieved over RuOx/Ru-ZIS under visible light irradiation, respectively, with an apparent quantum efficiency (AQE) of 4.36% at 400 nm. This work paves a new way to increase charge utilization by manipulating photocatalyst using single atom and clusters.

Atomically Dispersed Palladium Catalyst for Chemoselective Hydrogenation of Quinolines

Chemoselective hydrogenation of quinoline and its derivatives is a significant strategy to achieve the corresponding 1,2,3,4-tetrahydroquinolines (py-THQ) for various potential applications. Here, we precisely constructed a titanium carbide supported atomically dispersed Pd catalyst (PdSA+NC/TiC) for quinoline hydrogenation, delivering above 99% py-THQ selectivity at complete conversion with an outstanding turnover frequency (TOF) of 463 h-1. AC-HAADF-STEM and XAFS demonstrate that the atomic dispersion of Pd includes Pd-Ti2C2 single atoms and Pd clusters with atomic-layer thickness. Theoretical calculation and experimental results revealed that H2 dissociation and subsequent hydrogenation rates were greatly promoted over Pd clusters. Although the adsorption of quinolines and intermediates are easier on Pd clusters than on Pd single atoms, the desorption of py-THQ is more favored over Pd single atoms than over Pd clusters. The desorption step may be the main reason for 5,6,7,8-tetrahydroquinoline (bz-THQ) and decahydroquinoline (DHQ) formation. Thus, a low reaction activity and py-THQ selectivity were received over PdSA/TiC and PdNP/TiC, respectively.

Creating CoRu Dual Active Sites Codecorated Stable Porous Ceria Support for Enhanced Li-CO2 Batteries Cathodes

Lithium-carbon dioxide (Li-CO2) battery represents a high-energy density energy storage with excellent real-time CO2 enrichment and conversion, but its practical utilization is hampered by the development of an excellent catalytic cathode. Here, the synergistic catalytic strategy of designing CoRu bimetallic active sites achieves the electrocatalytic conversion of CO2 and the efficient decomposition of the discharge products, which in turn realizes the smooth operation of the Li-CO2 battery. Moreover, obtained support based on metal-organic frameworks precursors facilitates the convenient diffusion and adsorption of CO2, resulting in higher reaction concentration and lower mass transfer resistance. Meanwhile, the optimization of the interfacial electronic structure and the effective transfer of electrons are achieved by virtue of the strong interaction of CoRu at the support interface. As a result, the Li-CO2 cell assembled based on bimetallic CoRu active sites achieved a discharge capacity of 19,111 mA h g-1 and a steady-state discharge voltage of 2.58 V as well as a cycle life of >175 cycles at a rate of 100 mA g-1. Further experiments combined with density-functional theory calculations achieve a deeply view of the connection between cathode and electrochemical performance and pave a way for the subsequent development of advanced Li-CO2 catalytic cathodes.

A Rechargeable "Rocking Chair" Type Zn-CO2 Battery

Rising global temperatures and critical energy shortages have spurred researches into CO2 fixation and conversion within the realm of energy storage such as Zn-CO2 batteries. However, traditional Zn-CO2 batteries employ double-compartment electrolytic cells with separate carriers for catholytes and anolytes, diverging from the "rocking chair" battery mechanism. The specific energy of these conventional batteries is constrained by the solubility of discharge reactants/products in the electrolyte. Additionally, H2O molecules tend to trigger parasitic reactions at the electrolyte/electrode interfaces, undermining the long-term stability of Zn anodes. In this report, we introduce an innovative "rocking chair" type Zn-CO2 battery that utilizes a weak-acidic zinc trifluoromethanesulfonate aqueous electrolyte compatible with both cathode and anode. This design minimizes side reactions on the Zn surface and leverages the high catalytic activity of the cathode material, allowing the battery to achieve a substantial discharge capacity of 6734 mAh g-1 and maintain performance over 65 cycles. Moreover, the successful production of pouch cells demonstrates the practical applicability of Zn-CO2 batteries. Electrode characterizations confirm superior electrochemical reversibility, facilitated by solid discharge products of ZnCO3 and C. This work advances a "rocking chair" Zn-CO2 battery with an enhanced specific energy and a reversible pathway, providing a foundation for developing high-performance metal-CO2 batteries.

Enhanced catalytic performance through a single-atom preparation approach: a review on ruthenium-based catalysts

The outstanding catalytic properties of single-atom catalysts (SACs) stem from the maximum atom utilization and unique quantum size effects, leading to ever-increasing research interest in SACs in recent years. Ru-based SACs, which have shown excellent catalytic activity and selectivity, have been brought to the frontier of the research field due to their lower cost compared with other noble catalysts. The synthetic approaches for preparing Ru SACs are rather diverse in the open literature, covering a wide range of applications. In this review paper, we attempt to disclose the synthetic approaches for Ru-based SACs developed in the most recent years, such as defect engineering, coordination design, ion exchange, the dipping method, and electrochemical deposition etc., and discuss their representative applications in both electrochemical and organic reaction fields, with typical application examples given of: Li-CO2 batteries, N2 reduction, water splitting and oxidation of benzyl alcohols. The mechanisms behind their enhanced catalytic performance are discussed and their structure-property relationships are revealed in this review. Finally, future prospects and remaining unsolved issues with Ru SACs are also discussed so that a roadmap for the further development of Ru SACs is established.

An inorganic molten salt electrolyte-based Li-CO2 battery with moderate working temperature and enhanced performance

Herein, a binary inorganic molten salt electrolyte based on lithium bis(fluorosulfonyl)imide (LiFSI) and potassium bis(fluorosulfonyl)imide (KFSI) is applied to Li-CO2 batteries that can operate under 80 °C. Benefiting from the intrinsic nonvolatility, electrochemical stability, raised ionic conductivity, sufficient solubility and safety, the molten electrolyte endows the Li-CO2 battery with a large discharge capacity of 4612 mA h g-1 and superior rate capability. The introduction of the Ru@Super P carbon cathode further optimizes the discharge capacity (9503 mA h g-1), overpotential (1.15 V), and rate capability.

Ruthenium Nanoclusters and Single Atoms on α-MoC/N-Doped Carbon Achieves Low-Input/Input-Free Hydrogen Evolution via Decoupled/Coupled Hydrazine Oxidation

The hydrazine oxidation-assisted H2 evolution method promises low-input and input-free hydrogen production. However, developing high-performance catalysts for hydrazine oxidation (HzOR) and hydrogen evolution (HER) is challenging. Here, we introduce a bifunctional electrocatalyst α-MoC/N-C/RuNSA, merging ruthenium (Ru) nanoclusters (NCs) and single atoms (SA) into cubic α-MoC nanoparticles-decorated N-doped carbon (α-MoC/N-C) nanowires, through electrodeposition. The composite showcases exceptional activity for both HzOR and HER, requiring -80 mV and -9 mV respectively to reach 10 mA cm-2. Theoretical and experimental insights confirm the importance of two Ru species for bifunctionality: NCs enhance the conductivity, and its coexistence with SA balances the H ad/desorption for HER and facilitates the initial dehydrogenation during the HzOR. In the overall hydrazine splitting (OHzS) system, α-MoC/N-C/RuNSA excels as both anode and cathode materials, achieving 10 mA cm-2 at just 64 mV. The zinc hydrazine (Zn-Hz) battery assembled with α-MoC/N-C/RuNSA cathode and Zn foil anode can exhibit 97.3 % energy efficiency, as well as temporary separation of hydrogen gas during the discharge process. Therefore, integrating Zn-Hz with OHzS system enables self-powered H2 evolution, even in hydrazine sewage. Overall, the amalgamation of NCs with SA achieves diverse catalytic activities for yielding multifold hydrogen gas through advanced cell-integrated-electrolyzer system.

Steering the Orbital Hybridization to Boost the Redox Kinetics for Efficient Li-CO2 Batteries

The sluggish CO2 reduction and evolution reaction kinetics are thorny problems for developing high-performance Li-CO2 batteries. For the complicated multiphase reactions and multielectron transfer processes in Li-CO2 batteries, exploring efficient cathode catalysts and understanding the interplay between structure and activity are crucial to couple with these pendent challenges. In this work, we applied the CoS as a model catalyst and adjusted its electronic structure by introducing sulfur vacancies to optimize the d-band and p-band centers, which steer the orbital hybridization and boost the redox kinetics between Li and CO2, thus improving the discharge platform of Li-CO2 batteries and altering the deposition behavior of discharge products. As a result, a highly efficient bidirectional catalyst exhibits an ultrasmall overpotential of 0.62 V and a high energy efficiency of 82.8% and circulates stably for nearly 600 h. Meanwhile, density functional theory calculations and multiphysics simulations further elucidate the mechanism of bidirectional activity. This work not only provides a proof of concept to design a remarkably efficient catalyst but also sheds light on promoting the reversible Li-CO2 reaction by tailoring the electronic structure.

Advances of Synergistic Electrocatalysis Between Single Atoms and Nanoparticles/Clusters

Combining single atoms with clusters or nanoparticles is an emerging tactic to design efficient electrocatalysts. Both synergy effect and high atomic utilization of active sites in the composite catalysts result in enhanced electrocatalytic performance, simultaneously provide a radical analysis of the interrelationship between structure and activity. In this review, the recent advances of single-atomic site catalysts coupled with clusters or nanoparticles are emphasized. Firstly, the synthetic strategies, characterization, dynamics and types of single atoms coupled with clusters/nanoparticles are introduced, and then the key factors controlling the structure of the composite catalysts are discussed. Next, several clean energy catalytic reactions performed over the synergistic composite catalysts are illustrated. Eventually, the encountering challenges and recommendations for the future advancement of synergistic structure in energy-transformation electrocatalysis are outlined.

Work Function-Guided Electrocatalyst Design

The development of high-performance electrocatalysts for energy conversion reactions is crucial for advancing global energy sustainability. The design of catalysts based on their electronic properties (e.g., work function) has gained significant attention recently. Although numerous reviews on electrocatalysis have been provided, no such reports on work function-guided electrocatalyst design are available. Herein, a comprehensive summary of the latest advancements in work function-guided electrocatalyst design for diverse electrochemical energy applications is provided. This includes the development of work function-based catalytic activity descriptors, and the design of both monolithic and heterostructural catalysts. The measurement of work function is first discussed and the applications of work function-based catalytic activity descriptors for various reactions are fully analyzed. Subsequently, the work function-regulated material-electrolyte interfacial electron transfer (IET) is employed for monolithic catalyst design, and methods for regulating the work function and optimizing the catalytic performance of catalysts are discussed. In addition, key strategies for tuning the work function-governed material-material IET in heterostructural catalyst design are examined. Finally, perspectives on work function determination, work function-based activity descriptors, and catalyst design are put forward to guide future research. This work paves the way to the work function-guided rational design of efficient electrocatalysts for sustainable energy applications.

MOF-Derived CoSe2 Nanoparticles/Carbonized Melamine Foam as Catalytic Cathode Enabling Flexible Li-CO2 Batteries with High Energy Efficiency and Stable Cycling

Rechargeable aprotic Li-CO2 batteries have aroused worldwide interest owing to their environmentally friendly CO2 fixation ability and ultra-high specific energy density. However, its practical applications are impeded by the sluggish reaction kinetics and discharge product accumulation during cycling. Herein, a flexible composite electrode comprising CoSe2 nanoparticles embedded in 3D carbonized melamine foam (CoSe2/CMF) for Li-CO2 batteries is reported. The abundant CoSe2 clusters can not only facilitate CO2 reduction/evolution kinetics but also serve as Li2CO3 nucleation sites for homogeneous discharge product growth. The CoSe2/CMF-based Li-CO2 battery exhibits a large initial discharge capacity as high as 5.62 mAh cm-2 at 0.05 mA cm-2, a remarkably small voltage gap of 0.72 V, and an ultrahigh energy efficiency of 85.9% at 0.01 mA cm-2, surpassing most of the noble metal-based catalysts. Meanwhile, the battery demonstrates excellent cycling stability of 1620 h (162 cycles) at 0.02 mA cm-2 with an average overpotential of 0.98 V and energy efficiency of 85.4%. Theoretical investigations suggest that this outstanding performance is attributed to the suitable CO2/Li adsorption and low Li2CO3 decomposition energy. Moreover, flexible Li-CO2 pouch cell with CoSe2/CMF cathode displays stable power output under different bending deformations, showing promising potential in wearable electronic devices.

Cross-linked K0.5MnO2 nanoflower composites for high rate and low overpotential Li-CO2 batteries

Rechargeable Li-CO2 batteries are deemed to be attractive energy storage systems, as they can effectively inhale and fix carbon dioxide and possess an extremely high energy density. Unfortunately, the irreversible decomposition of the insoluble and insulating Li2CO3 results in awful electrochemical performance and inferior energy efficiency of Li-CO2 batteries. Furthermore, the low energy efficiency will exacerbate the extra waste of resources. Therefore, it is vital to design novel and efficient catalysts to enhance the battery performance. Herein, a facile, one-step strategy is introduced to design cross-linked, ultrathin K0.5MnO2 nanoflowers combined with CNTs (K0.5MnO2/CNT) as a highly efficient cathode for Li-CO2 batteries. Impressively, the Li-CO2 battery based on the K0.5MnO2/CNT cathode achieves a low overpotential (1.05 V) and a high average energy efficiency (87.95%) at a current density of 100 mA g-1. Additionally, the K0.5MnO2/CNT cathode can steadily run for over 100 cycles (overpotential < 1.20 V). Moreover, a low overpotential of 1.47 V can be obtained even at a higher current density of 1000 mA g-1, indicating the superior rate performance of K0.5MnO2/CNT. This strategy offers new insight and guidance for the development of low-cost and high-performance Li-CO2 batteries.

High Entropy Alloys Enable Durable and Efficient Lithium-Mediated CO2 Redox Reactions

Designing electrocatalysts with high activity and durability for multistep reduction and oxidation reactions is challenging. High-entropy alloys (HEAs) are intriguing due to their tunable geometric and electronic structure through entropy effects. However, understanding the origin of their exceptional performance and identifying active centers is hindered by the diverse microenvironment in HEAs. Herein, NiFeCoCuRu HEAs designed with an average diameter of 2.17 nm, featuring different adsorption capacities for various reactants and intermediates in Li-mediated CO2 redox reactions, are introduced. The electronegativity-dependent nature of NiFeCoCuRu HEAs induces significant charge redistribution, shifting the d-band center closer to Fermi level and forming highly active clusters of Ru, Co, and Ni for Li-based compounds adsorptions. This lowers energy barriers and simultaneously stabilizes *LiCO2 and LiCO3+CO intermediates, enhancing the efficiency of both CO2 reduction and Li2CO3 decomposition over extended periods. This work provides insights into specific active site interactions with intermediates, highlighting the potential of HEAs as promising catalysts for intricate CO2 redox reactions.

Bonobo Optimizer: A New Tool Toward the Global Optimization of Small Atomic Clusters

In the realm of structural and bonding investigations within chemical systems, elucidating global minimum energy configurations stands as a paramount goal. As the systems increase in size and complexity, this pursuit becomes progressively challenging. Herein, we introduce Bonobo optimizer (BO), a metaheuristic algorithm inspired by the social and reproductive behaviors of bonobos, to the domain of chemical problem solving. Focusing on small carbon clusters, this study systematically evaluates BO's performance, showcasing its robustness and efficiency. Parametric studies highlight the algorithm's adaptability, consistently converging to global minimum structures. Rigorous statistical validation supports the results, and a comparative analysis against established global optimization algorithms underlines BO's superior efficiency. This exploration extends the applicability of BO to the optimization of atomic clusters, providing a promising avenue for future advancements in computational chemistry.

Selectivity-Enhanced Electroreduction of CO2 to CO at Novel Ru-Linked-GO Nanohybrids: the Role of Nanoarchitecture

Recently, global-scale efforts have been conducted for the electroreduction of CO2 as a potentially beneficial pathway for the conversion of greenhouse gases to useful chemicals and renewable fuels. This study focuses on the development of selective and sustainable electrocatalysts for the reduction of aqueous CO2 to CO. A RuIIcomplex [Ru(tptz)(ACN)Cl2] (RCMP) (tptz = 2,4,6-tris(2-pyridyl)-1,3,5-triazine, ACN = acetonitrile) was prepared as a molecular electrocatalyst for the CO2 reduction reaction in an aqueous solution. Density functional theory-calculated frontier molecular orbitals suggested that the tptz ligand plays a key role in dictating the electrocatalytic reactions. The RCMP electrocatalyst was grafted onto the graphene oxide (GO) surface both noncovalently (GO/RCMP) and covalently (GO-RCMP). The field emission scanning electron microscopy and elemental distribution analyses revealed the homogeneous distribution of the complex onto the GO sheet. The photoluminescence spectra confirmed accelerated charge-transfer in both nanohybrids. Compared to the bare complex, the GO-RCMP and GO/RCMP nanohybrids showed enhanced electrocatalytic activity, achieving >95% and 90% Faradaic efficiencies for CO production at more positive onset potentials, respectively. The GO-RCMP nanohybrid demonstrated outstanding electrocatalytic activity with a current of ∼84 μA. The study offers a perspective on outer- and inner-sphere electron-transfer mechanisms for electrochemical energy conversion systems.

Surface Engineered Single-atom Systems for Energy Conversion

Single-atom catalysts (SACs) are demonstrated to show exceptional reactivity and selectivity in catalytic reactions by effectively utilizing metal species, making them a favorable choice among the different active materials for energy conversion. However, SACs are still in the early stages of energy conversion, and problems like agglomeration and low energy conversion efficiency are hampering their practical applications. Substantial research focus on support modifications, which are vital for SAC reactivity and stability due to the intimate relationship between metal atoms and support. In this review, a category of supports and a variety of surface engineering strategies employed in SA systems are summarized, including surface site engineering (heteroatom doping, vacancy introducing, surface groups grafting, and coordination tunning) and surface structure engineering (size/morphology control, cocatalyst deposition, facet engineering, and crystallinity control). Also, the merits of support surface engineering in single-atom systems are systematically introduced. Highlights are the comprehensive summary and discussions on the utilization of surface-engineered SACs in diversified energy conversion applications including photocatalysis, electrocatalysis, thermocatalysis, and energy conversion devices. At the end of this review, the potential and obstacles of using surface-engineered SACs in the field of energy conversion are discussed. This review aims to guide the rational design and manipulation of SACs for target-specific applications by capitalizing on the characteristic benefits of support surface engineering.

Accelerating the Phase Formation Kinetics of Alluaudite Sodium Iron Sulfate Cathodes via Ultrafast Thermal Shock

Alluaudite sodium iron sulfate (NFS) exhibits great potential for use in sodium-ion battery cathodes due to its elevated operating potential and abundant element reserves. However, conventional solid-state methods demonstrate a low heating/cooling rate and sluggish reaction kinetics, requiring a long thermal treatment to effectively fabricate NFS cathodes. Herein, we propose a thermal shock (TS) strategy to synthesize alluaudite sodium iron sulfate cathodes using either hydrous or anhydrous raw materials. The analysis of the phase formation process reveals that TS treatment can significantly facilitate the removal of crystal water and decomposition of the intermediate phase Na2Fe(SO4)2 in the hydrous precursor. In the case of the anhydrous precursor, the kinetics of the combination reaction between Na2SO4 and FeSO4 can be also accelerated by TS treatment. Consequently, pure NFS phase formation can be completed after a substantially shorter time of post-sintering, thereby saving significant time and energy. The TS-treated NFS cathode derived from hydrous precursor exhibits higher retention after 200 cycles at 1C and better rate capability than the counterpart prepared by conventional long-term tube furnace sintering, demonstrating the great potential of this novel strategy.

Deciphering the contributing motifs of reconstructed cobalt (II) sulfides catalysts in Li-CO2 batteries

Developing highly efficient catalysts is significant for Li-CO2 batteries. However, understanding the exact structure of catalysts during battery operation remains a challenge, which hampers knowledge-driven optimization. Here we use X-ray absorption spectroscopy to probe the reconstruction of CoSx (x = 8/9, 1.097, and 2) pre-catalysts and identify the local geometric ligand environment of cobalt during cycling in the Li-CO2 batteries. We find that different oxidized states after reconstruction are decisive to battery performance. Specifically, complete oxidation on CoS1.097 and Co9S8 leads to electrochemical performance deterioration, while oxidation on CoS2 terminates with Co-S4-O2 motifs, leading to improved activity. Density functional theory calculations show that partial oxidation contributes to charge redistributions on cobalt and thus facilitates the catalytic ability. Together, the spectroscopic and electrochemical results provide valuable insight into the structural evolution during cycling and the structure-activity relationship in the electrocatalyst study of Li-CO2 batteries.

Single-atom tailored atomically-precise nanoclusters for enhanced electrochemical reduction of CO2-to-CO activity

The development of facile tailoring approach to adjust the intrinsic activity and stability of atomically-precise metal nanoclusters catalysts is of great interest but remians challenging. Herein, the well-defined Au8 nanoclusters modified by single-atom sites are rationally synthesized via a co-eletropolymerization strategy, in which uniformly dispersed metal nanocluster and single-atom co-entrenched on the poly-carbazole matrix. Systematic characterization and theoretical modeling reveal that functionalizing single-atoms enable altering the electronic structures of Au8 clusters, which amplifies their electrocatalytic reduction of CO2 to CO activity by ~18.07 fold compared to isolated Au8 metal clusters. The rearrangements of the electronic structure not only strengthen the adsorption of the key intermediates *COOH, but also establish a favorable reaction pathway for the CO2 reduction reaction. Moreover, this strategy fixing nanoclusters and single-atoms on cross-linked polymer networks efficiently deduce the performance deactivation caused by agglomeration during the catalytic process. This work contribute to explore the intrinsic activity and stability improvement of metal clusters.

Real-time tracking of electron transfer at catalytically active interfaces in lithium-ion batteries

Transition metals and related compounds are known to exhibit high catalytic activities in various electrochemical reactions thanks to their intriguing electronic structures. What is lesser known is their unique role in storing and transferring electrons in battery electrodes which undergo additional solid-state conversion reactions and exhibit substantially large extra capacities. Here, a full dynamic picture depicting the generation and evolution of electrochemical interfaces in the presence of metallic nanoparticles is revealed in a model CoCO3/Li battery via an in situ magnetometry technique. Beyond the conventional reduction to a Li2CO3/Co mixture under battery operation, further decomposition of Li2CO3 is realized by releasing interfacially stored electrons from its adjacent Co nanoparticles, whose subtle variation in the electronic structure during this charge transfer process has been monitored in real time. The findings in this work may not only inspire future development of advanced electrode materials for next-generation energy storage devices but also open up opportunities in achieving in situ monitoring of important electrocatalytic processes in many energy conversion and storage systems.

Enabling All-Solid-State Lithium-Carbon Dioxide Battery Operation in a Wide Temperature Range

Flexible all-solid-state lithium-carbon dioxide batteries (FASSLCBs) are recognized as a next-generation energy storage technology by solving safety and shuttle effect problems. However, the present FASSLCBs rely heavily on high-temperature operation due to sluggish solid-solid-gas multiphase mass transfer and unclear capacity degradation mechanism. Herein, we designed bicontinuous hierarchical porous structures (BCHPSs) for both solid polymer electrolyte and cathode for FASSLCBs to facilitate the mass transfer in all connected directions. The formed large Lewis acidic surface effectively promotes the lithium salt dissociation and the CO2 conversion. Furthermore, it is unraveled that the battery capacity degradation originates from the "dead Li2CO3" formation, which is inhibited by the fast decomposition of Li2CO3. Accordingly, the assembled FASSLCBs exhibit an excellent cycling stability of 133 cycles at 60 °C, which is 2.7 times longer than that without BCHPSs, and the FASSLCBs can be operated repeatedly even at room temperature. This BCHPS method and fundamental deactivation mechanism provide a perspective for designing FASSLCBs with long cycling life.

Energy Band Engineering Guided Design of Bidirectional Catalyst for Reversible Li-CO2 Batteries

Li-CO2 batteries arouse great interest in the context of carbon neutralization, but their practicability is severely hindered by the sluggish CO2 redox reaction kinetics at the cathode, which brings about formidable challenges such as high overpotential and low Coulombic efficiency. For the complex multi-electron transfer process, the design of catalysts at the molecular or atomic level and the understanding of the relationship between electron state and performance are essential for the CO2 redox. However, little attention is paid to it. In this work, using Co3 S4 as a model system, density functional theory (DFT) calculations reveal that the adjusted d-band and p-band centers of Co3 S4 with the introduction of Cu and sulfur vacancies are hybridized between CO2 and Li species, respectively, which is conducive to the adsorption of reactants and the decomposition of Li2 CO3 , and the experimental results further verify the effectiveness of energy band engineering. As a result, a highly efficient bidirectional catalyst is produced and shows an ultra-small voltage gap of 0.73 V and marvelous Coulombic efficiency of 92.6%, surpassing those of previous catalysts under similar conditions. This work presents an effective catalyst design and affords new insight into the high-performance cathode catalyst materials for Li-CO2 batteries.

Nanoscale Metal Particle Modified Single-Atom Catalyst: Synthesis, Characterization, and Application

Single-atom catalysts (SACs) have attracted considerable attention in heterogeneous catalysis because of their well-defined active sites, maximum atomic utilization efficiency, and unique unsaturated coordinated structures. However, their effectiveness is limited to reactions requiring active sites containing multiple metal atoms. Furthermore, the loading amounts of single-atom sites must be restricted to prevent aggregation, which can adversely affect the catalytic performance despite the high activity of the individual atoms. The introduction of nanoscale metal particles (NMPs) into SACs (NMP-SACs) has proven to be an efficient approach for improving their catalytic performance. A comprehensive review is urgently needed to systematically introduce the synthesis, characterization, and application of NMP-SACs and the mechanisms behind their superior catalytic performance. This review first presents and classifies the different mechanisms through which NMPs enhance the performance of SACs. It then summarizes the currently reported synthetic strategies and state-of-the-art characterization techniques of NMP-SACs. Moreover, their application in electro/thermo/photocatalysis, and the reasons for their superior performance are discussed. Finally, the challenges and perspectives of NMP-SACs for the future design of advanced catalysts are addressed.

Recent Progress in Hot Spot Regulated Strategies for Catalysts Applied in Li-CO2 Batteries

As a high energy density power system, lithium-carbon dioxide (Li-CO2 ) batteries play an important role in addressing the fossil fuel crisis issues and alleviating the greenhouse effect. However, the sluggish transformation kinetic of CO2 and the difficult decomposition of discharge products impede the achievement of large capacity, small overpotential, and long life span of the batteries, which require exploring efficient catalysts to resolve these problems. In this review, the main focus is on the hot spot regulation strategies of the catalysts, which include the modulation of the active sites, the designing of microstructure, and the construction of composition. The recent progress of promising catalysis with hot spot regulated strategies is systematically addressed. Critical challenges are also presented and perspectives to provide useful guidance for the rational design of highly efficient catalysts for practical advanced Li-CO2 batteries are proposed.

Hydroxyl-Bonded Ru on Metallic TiN Surface Catalyzing CO2 Reduction with H2O by Infrared Light

Synchronized conversion of CO2 and H2O into hydrocarbons and oxygen via infrared-ignited photocatalysis remains a challenge. Herein, the hydroxyl-coordinated single-site Ru is anchored precisely on the metallic TiN surface by a NaBH4/NaOH reforming method to construct an infrared-responsive HO-Ru/TiN photocatalyst. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (ac-HAADF-STEM) and X-ray absorption spectroscopy (XAS) confirm the atomic distribution of the Ru species. XAS and density functional theory (DFT) calculations unveil the formation of surface HO-RuN5-Ti Lewis pair sites, which achieves efficient CO2 polarization/activation via dual coordination with the C and O atoms of CO2 on HO-Ru/TiN. Also, implanting the Ru species on the TiN surface powerfully boosts the separation and transfer of photoinduced charges. Under infrared irradiation, the HO-Ru/TiN catalyst shows a superior CO2-to-CO transformation activity coupled with H2O oxidation to release O2, and the CO2 reduction rate can further be promoted by about 3-fold under simulated sunlight. With the key reaction intermediates determined by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and predicted by DFT simulations, a possible photoredox mechanism of the CO2 reduction system is proposed.

Metal Alloys-Structured Electrocatalysts: Metal-Metal Interactions, Coordination Microenvironments, and Structural Property-Reactivity Relationships

Metal alloys-structured electrocatalysts (MAECs) have made essential contributions to accelerating the practical applications of electrocatalytic devices in renewable energy systems. However, due to the complex atomic structures, varied electronic states, and abundant supports, precisely decoding the metal-metal interactions and structure-activity relationships of MAECs still confronts great challenges, which is critical to direct the future engineering and optimization of MAECs. Here, this timely review comprehensively summarizes the latest advances in creating the MAECs, including the metal-metal interactions, coordination microenvironments, and structure-activity relationships. First, the fundamental classification, design, characterization, and structural reconstruction of MAECs are outlined. Then, the electrocatalytic merits and modulation strategies of recent breakthroughs for noble and non-noble metal-structured MAECs are thoroughly discussed, such as solid solution alloys, intermetallic alloys, and single-atom alloys. Particularly, unique insights into the bond interactions, theoretical understanding, and operando techniques for mechanism disclosure are given. Thereafter, the current states of diverse MAECs with a unique focus on structural property-reactivity relationships, reaction pathways, and performance comparisons are discussed. Finally, the future challenges and perspectives for MAECs are systematically discussed. It is believed that this comprehensive review can offer a substantial impact on stimulating the widespread utilization of metal alloys-structured materials in electrocatalysis.

Hydrogen-Bonded Organic Framework to Upgrade Cycling Stability and Rate Capability of Li-CO2 Batteries

Elaborately designed multifunctional electrocatalysts capable of promoting Li+ and CO2 transport are essential for upgrading the cycling stability and rate capability of Li-CO2 batteries. Hydrogen-bonded organic frameworks (HOFs) with open channels and easily functionalized surfaces hold great potential for applications in efficient cathodes of Li-CO2 batteries. Herein, a robust HOFS (HOF-FJU-1) is introduced for the first time as a co-catalyst in the cathode material of Li-CO2 batteries. HOF-FJU-1 with cyano groups located periodically in the pore can induce homogeneous deposition of discharge products and accommodate volumetric expansion of discharge products during cycling. Besides, HOF-FJU-1 enables effective interaction between Ru0 nanoparticles and cyano groups, thus forming efficient and uniform catalytic sites for CRR/CER. Moreover, HOF-FJU-1 with regularly arranged open channels are beneficial for CO2 and Li+ transport, enabling rapid redox kinetic conversion of CO2 . Therefore, the HOF-based Li-CO2 batteries are capable of stable operation at 400 mA g-1 for 1800 h and maintain a low overpotential of 1.96 V even at high current densities up to 5 A g-1 . This work provides valuable guidance for developing multifunctional HOF-based catalysts to upgrade the longevity and rate capability of Li-CO2 batteries.

Halogenated Functional Electrolyte Additive for Li-CO2 Batteries

In recent years, functional electrolyte additives have been widely studied during the CO2 evolution reaction (CO2ER) and CO2 reduction reaction (CO2RR) processes for Li-CO2 batteries. Owing to different concerns, functions of these additives are also multiple and limited. In this work, the multiple impacts of functional electrolyte additives for Li-CO2 batteries are discussed. N-phenylpyrrolidine (PPD) and 1-(3-bromophenyl) pyrrole (Br-PPD) are investigated as additives successively. First, the corresponding charging potential during the CO2ER process can be reduced to 3.65 V with PPD; then the Li||Li symmetric cells with Br-PPD possess a superior long-term cycling of 800 h benefited from a stable solid electrolyte interphase (SEI) on the surface of a Li metal by using a Li anode protected with bromine functional groups. In Br-PPD-based Li-CO2 cells, the charging potential can be maintained at 3.70 V for 120 cycles even with a Super P cathode. In this work, the relationship between the structural properties of organic molecules and their electrochemical applications is discussed and investigated. This is essential for the targeted design and preparation of additives in rechargeable batteries.

In Situ Preparation of Polyamine-Derived Ru Cluster@N-Doped Porous Carbon Nanoplates for Hydrogen Evolution over Wide pH Ranges

Efficient and low-cost electrocatalysts for the hydrogen evolution reaction (HER) are required for producing hydrogen energy through water splitting. Carbon materials as HER catalyst supports are explored widely since the strong metal-support interactions are generally believed to be active and stable toward HER. Herein, we report N-doped porous carbon materials as novel substrates to stabilize the cluster metal sites through the Ru(III) polyamine complexes, which play an important role not only in efficient electron transfer but also in the increasing utilization of metallic active sites. Meanwhile, due to the strong metal-support interactions driven by Ru(III) polyamine complexes, the obtained Ru cluster with a mass loading of 3% on N-doped porous carbon nanoplates (Ru cluster@NCs) exhibits robust stability for HER at a constant voltage, proving to be a promising candidate catalyst for HER. Density functional theory calculations further indicate that the Gibbs free energy (ΔG) of adsorbed H* of Ru cluster@NCs is much closer to zero compared to Ru@(10%)NCs and Pt/C(20%), thus Ru cluster@NCs facilitate the HER process.

Dual-Active-Sites Single-Atom Catalysts for Advanced Applications

Dual-Active-Sites Single-Atom catalysts (DASs SACs) are not only the improvement of SACs but also the expansion of dual-atom catalysts. The DASs SACs contains dual active sites, one of which is a single atomic active site, and the other active site can be a single atom or other type of active site, endowing DASs SACs with excellent catalytic performance and a wide range of applications. The DASs SACs are categorized into seven types, including the neighboring mono metallic DASs SACs, bonded DASs SACs, non-bonded DASs SACs, bridged DASs SACs, asymmetric DASs SACs, metal and nonmetal combined DASs SACs and space separated DASs SACs. Based on the above classification, the general methods for the preparation of DASs SACs are comprehensively described, especially their structural characteristics are discussed in detail. Meanwhile, the in-depth assessments of DASs SACs for variety applications including electrocatalysis, thermocatalysis and photocatalysis are provided, as well as their unique catalytic mechanism are addressed. Moreover, the prospects and challenges for DASs SACs and related applications are highlighted. The authors believe the great expectations for DASs SACs, and this review will provide novel conceptual and methodological perspectives and exciting opportunities for further development and application of DASs SACs.

p-Block Bismuth Nanoclusters Sites Activated by Atomically Dispersed Bismuth for Tandem Boosting Electrocatalytic Hydrogen Peroxide Production

Constructing electrocatalysts with p-block elements is generally considered rather challenging owing to their closed d shells. Here for the first time, we present a p-block-element bismuth-based (Bi-based) catalyst with the co-existence of single-atomic Bi sites coordinated with oxygen (O) and sulfur (S) atoms and Bi nanoclusters (Biclu ) (collectively denoted as BiOSSA /Biclu ) for the highly selective oxygen reduction reaction (ORR) into hydrogen peroxide (H2 O2 ). As a result, BiOSSA /Biclu gives a high H2 O2 selectivity of 95 % in rotating ring-disk electrode, and a large current density of 36 mA cm-2 at 0.15 V vs. RHE, a considerable H2 O2 yield of 11.5 mg cm-2 h-1 with high H2 O2 Faraday efficiency of ∼90 % at 0.3 V vs. RHE and a long-term durability of ∼22 h in H-cell test. Interestingly, the experimental data on site poisoning and theoretical calculations both revealed that, for BiOSSA /Biclu , the catalytic active sites are on the Bi clusters, which are further activated by the atomically dispersed Bi coordinated with O and S atoms. This work demonstrates a new synergistic tandem strategy for advanced p-block-element Bi catalysts featuring atomic-level catalytic sites, and the great potential of rational material design for constructing highly active electrocatalysts based on p-block metals.

Recent Advances in Rechargeable Metal-CO2 Batteries with Nonaqueous Electrolytes

This review article discusses the recent advances in rechargeable metal-CO2 batteries (MCBs), which include the Li, Na, K, Mg, and Al-based rechargeable CO2 batteries, mainly with nonaqueous electrolytes. MCBs capture CO2 during discharge by the CO2 reduction reaction and release it during charging by the CO2 evolution reaction. MCBs are recognized as one of the most sophisticated artificial modes for CO2 fixation by electrical energy generation. However, extensive research and substantial developments are required before MCBs appear as reliable, sustainable, and safe energy storage systems. The rechargeable MCBs suffer from the hindrances like huge charging-discharging overpotential and poor cyclability due to the incomplete decomposition and piling of the insulating and chemically stable compounds, mainly carbonates. Efficient cathode catalysts and a suitable architectural design of the cathode catalysts are essential to address this issue. Besides, electrolytes also play a vital role in safety, ionic transportation, stable solid-electrolyte interphase formation, gas dissolution, leakage, corrosion, operational voltage window, etc. The highly electrochemically active metals like Li, Na, and K anodes severely suffer from parasitic reactions and dendrite formation. Recent research works on the aforementioned secondary MCBs have been categorically reviewed here, portraying the latest findings on the key aspects governing secondary MCB performances.

Intrinsic Descriptor Guided Noble Metal Cathode Design for Li-CO2 Battery

To date, the effect of noble metal (NM) electronic structures on CO2 reaction activity remains unknown, and explicit screening criteria are still lacking for designing highly efficient catalysts in CO2 -breathing batteries. Herein, by preferentially considering the decomposition of key intermediate Li2 CO3 , an intrinsic descriptor constituted of thed x 2 - y 2 ${{\rm{d}}}_{{x}^2 - {y}^2}$ orbital states and the electronegativity for predicting high-performance cathode material are discovered. As a demonstration, a series of graphene-supported noble metals (NM@G) as cathodes are fabricated via a fast laser scribing technique. Consistent with the preliminary prediction, Pd@G exhibits an ultralow overpotential (0.41 V), along with superior cycling performance up to 1400 h. Moreover, the overall thermodynamic reaction pathways on NM@G confirm the reliability of the established intrinsic descriptor. This basic finding of the relationship between the electronic properties of noble metal cathodes and the performance of Li-CO2 batteries provides a novel avenue for designing remarkably efficient cathode materials for metal-CO2 batteries.

Revisiting the Role of Discharge Products in Li-CO2 Batteries

Rechargeable lithium-carbon dioxide (Li-CO2 ) batteries are promising devices for CO2 recycling and energy storage. However, thermodynamically stable and electrically insulating discharge products (DPs) (e.g., Li2 CO3 ) deposited at cathodes require rigorous conditions for completed decomposition, resulting in large recharge polarization and poor battery reversibility. Although progress has been achieved in cathode design and electrolyte optimization, the significance of DPs is generally underestimated. Therefore, it is necessary to revisit the role of DPs in Li-CO2 batteries to boost overall battery performance. Here, a critical and systematic review of DPs in Li-CO2 batteries is reported for the first time. Fundamentals of reactions for formation and decomposition of DPs are appraised; impacts on battery performance including overpotential, capacity, and stability are demonstrated; and the necessity of discharge product management is highlighted. Practical in situ/operando technologies are assessed to characterize reaction intermediates and the corresponding DPs for mechanism investigation. Additionally, achievable control measures to boost the decomposition of DPs are evidenced to provide battery design principles and improve the battery performance. Findings from this work will deepen the understanding of electrochemistry of Li-CO2 batteries and promote practical applications.

Cooperation between Dual Metal Atoms and Nanoclusters Enhances Activity and Stability for Oxygen Reduction and Evolution

We have achieved the synthesis of dual-metal single atoms and atomic clusters that co-anchor on a highly graphitic carbon support. The catalyst comprises Ni₄ (and Fe₄) nanoclusters located adjacent to the corresponding NiN₄ (and FeN₄) single-atom sites, which is verified by systematic X-ray absorption characterization and density functional theory calculations. A distinct cooperation between Fe₄ (Ni₄) nanoclusters and the corresponding FeN₄ (NiN₄) atomic sites optimizes the adsorption energy of reaction intermediates and reduces the energy barrier of the potential-determining steps. This catalyst exhibits enhanced oxygen reduction and evolution activity and long-cycle stability compared to counterparts without nanoclusters and commercial Pt/C. The fabricated Zn-air batteries deliver a high power density and long-term cyclability, demonstrating their prospects in energy storage device applications.

Mo2 N-ZrO2 Heterostructure Engineering in Freestanding Carbon Nanofibers for Upgrading Cycling Stability and Energy Efficiency of Li-CO2 Batteries

Li-CO₂ batteries have attracted considerable attention for their advantages of CO₂ fixation and high energy density. However, the sluggish dynamics of CO₂ reduction/evolution reactions restrict the practical application of Li-CO₂ batteries. Herein, a dual-functional Mo₂ N-ZrO₂ heterostructure engineering in conductive freestanding carbon nanofibers (Mo₂ N-ZrO₂ @NCNF) is reported. The integration of Mo₂ N-ZrO₂ heterostructure in porous carbons provides the opportunity to simultaneously accelerate electron transport, boost CO₂ conversion, and stabilize intermediate discharge product Li₂ C₂ O₄ . Benefiting from the synchronous advantages, the Mo₂ N-ZrO₂ @NCNF catalyst endows the Li-CO₂ batteries with excellent cycle stability, good rate capability, and high energy efficiency even under high current densities. The designed cathodes exhibit an ultrahigh energy efficiency of 89.8% and a low charging voltage below 3.3 V with a potential gap of 0.32 V. Remarkably, stable operation over 400 cycles can be achieved even at high current densities of 50 µA cm^-2 . This work provides valuable guidance for developing multifunctional heterostructured catalysts to upgrade longevity and energy efficiency of Li-CO₂ batteries.

Tailored Heterojunction Active Sites for Oxygen Electrocatalyst Promotion in Zinc-Air Batteries

Rechargeable zinc-air batteries (ZABs) are promising energy storage systems due to their low-cost and safety. However, the working principle of ZABs is based on oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), which display sluggish kinetic and low stability. Herein, this work proposes a novel method to design a heterogeneous CoP/CoO electrocatalyst on mesopore nanobox carbon/carbon nanotube (CoP/CoO@MNC-CNT) that enriched active sites and synergistic effect. Moreover, the well-defined heterointerfaces could lower the energy barrier for intermediate species adsorption and promote OER and ORR electrochemical performances. The CoP/CoO@MNC-CNT electrocatalyst presents a high half-wave potential of 0.838 V for ORR and a small overpotential of 270 mV for OER. The ZABs-based CoP/CoO@MNC-CNT air-cathode shows an open-circuit voltage of 1.409 V, the long-term cycle life of 500 h with a small voltage difference change of 7.7%. Additionally, the flexible ZABs exhibit highly mechanical stability, demonstrating their application potential in wearable electronic devices.

Atomically Dispersed Manganese on Carbon Substrate for Aqueous and Aprotic CO2 Electrochemical Reduction

CO₂ utilization and conversion are of great importance in alleviating the rising CO₂ concentration in the atmosphere. Here, a single-atom catalyst (SAC) is reported for electrochemical CO₂ utilization in both aqueous and aprotic electrolytes. Specifically, atomically dispersed Mn-N₄ sites are embedded in bowl-like mesoporous carbon particles with the functionalization of epoxy groups in the second coordination spheres. Theoretical calculations suggest that the epoxy groups near the Mn-N₄ site adjust the electronic structure of the catalyst with reduced reaction energy barriers for the electrocatalytic reduction of CO₂ to CO. The resultant Mn-single-atom carbon with N and O doped catalyst (MCs-(N,O)) exhibits extraordinary electrocatalytic performance with a high CO faradaic efficiency of 94.5%, a high CO current density of 13.7 mA cm^-2 , and a low overpotential of 0.44 V in the aqueous environment. Meanwhile, as a cathode catalyst for aprotic Li-CO₂ batteries, the MCs-(N,O) with well-regulated active sites and unique mesoporous bowl-like morphology optimizes the nucleation behavior of discharge products. MCs-(N,O)-based batteries deliver a low overpotential and excellent cyclic stability of 1000 h. The findings in this work provide a new avenue to design and fabricate SACs for various electrochemical CO₂ utilization systems.

Oxygen-Loss-Induced Structural Degradation in ε-LiVOPO4

The ε-LiVOPO₄ cathode for Li-ion batteries has attracted wide attention with its multivalent electronic states and improved discharge capacity of over 300 mAh/g. Oxygen loss stands as a potential cause for structural degradations of the ε-LiVOPO₄ cathode and its derivatives but has been barely studied. Through in situ environmental transmission electron microscopy, we probe lattice oxygen loss and the associated structural degradations by spatially and temporally resolving the atomic-scale structural dynamics and phase transformation pathways in ε-LiVOPO₄. We demonstrate that the mild oxygen loss at 400 °C induces a topotactic phase transformation of ε-LiVOPO₄ → α-Li₃V₂(PO₄)₃ in the particle surface via a nucleation and growth mechanism, leading to the formation of a core-shell configuration. The phase transformation can be reversed by switching to an oxidizing environment, in which the α-Li₃V₂(PO₄)₃ is reoxidized to ε-LiVOPO₄. By contrast, oxygen loss at higher temperatures of 500 and 600 °C results in a high concentration of oxygen vacancies that subsequently induces irreversible structural damages including lattice amorphization and formation of nanocavities. This work illustrates the fundamental mechanisms governing the structural failure of oxide cathodes and underlines possible strategies to overcome such issues by exploiting environmental constraints.