Reconstruction of Thiospinel to Active Sites and Spin Channels for Water Oxidation

In Situ Reconfigured Heterostructure Active Sites on Transition Metal Sulfides Heterojunction for Accelerated Water Oxidation

Transition metal sulfides (TMSs) are promising noble-metal-free electrocatalysts for electrochemical water splitting due to their distinctive physical and chemical properties, but they usually undergo complicated structure reconfiguration during the oxygen evolution reaction (OER). Precisely controlling the in situ reconfiguration of TMSs for in situ generation of high-activity real active sites still remains a great challenge. Herein, we propose to in situ reconfigure heterostructure active-sites on transition metal sulfides via heterojunction engineering and achieve high OER performances on (Ni,Fe)S2/MoS2 catalysts. The continuous leaching of Mo and S during electrooxidation induces the reconfiguration, and the strong electronic interaction of (Ni,Fe)S2 and MoS2 generates the special Ni(OH)2/NiOOH/FeOOH heterostructure sites via an asynchronous reconfiguration of Fe and Ni. The (Ni,Fe)S2/MoS2 heterostructure catalyst therefore exhibits excellent OER activity (a small overpotential of 228 mV at 100 mA cm-2) and a low voltage in an alkaline water electrolyzer (1.44 V at 10 mA cm-2), outperforming the homogeneous Mo-free NiFe sulfide catalysts with conventional reconfiguration of Ni-doped FeOOH. This work sheds light on the precise structures design under complicated electrochemical reconstruction and broadens the horizon of reconstruction chemistry to design low-cost and efficient electrocatalysts.

Fe doping intensifies the built-in electric field for tailoring the reconstruction of sulfides towards efficient oxygen evolution

The traditional view of sulfides as stable active centers has hindered the development of a clear structure-activity relationship and the rational design of high-performance oxygen evolution reaction (OER) catalysts. In this study, we focus on regulating sulfide reconstruction and have synthesized a Fe-Ni3S4/Cr2O3 pre-catalyst. Under the combined influence of the built-in electric field (BIEF) at the heterogeneous interface and Fe doping, both the sulfide reconstruction process and the electronic structure of the reconstructed product, namely Fe-NiOOH, were effectively tuned. The enhanced BIEF induced by Fe doping generated electron-rich regions on the sulfide surface, stabilizing the reconstruction process. Fe doping into the sulfide induced the incorporation of Fe into NiOOH, modulating the electronic states near the Fermi level of the metal-oxygen bond and subsequently activating the lattice oxygen mediated mechanism (LOM) of Fe-NiOOH, which serves as the true active center. Additionally, the BIEF optimized OH- diffusion dynamics and the energy consumption of hydroxyl deprotonation, reducing the energy barrier of the rate-limiting step of the LOM process, further enhancing OER activity. Remarkably, Fe-Ni3S4/Cr2O3 demonstrated excellent OER activity and commercial viability. This work offers a new perspective on the regulation of reconstruction products of pre-catalyst, providing fresh insights for the design of efficient OER catalysts.

Rational design of precatalysts and controlled evolution of catalyst-electrolyte interface for efficient hydrogen production

The concept of precatalyst is widely accepted in electrochemical water splitting, but the role of precatalyst activation and the resulted changes of electrolyte composition is often overlooked. Here, we elucidate the impact of potential-dependent changes for both precatalyst and electrolyte using Co2Mo3O8 as a model system. Potential-dependent reconstruction of Co2Mo3O8 precatalyst results in an electrochemically stable Co(OH)2@Co2Mo3O8 catalyst and additional Mo dissolved as MoO42- into electrolyte. The Co(OH)2/Co2Mo3O8 interface accelerates the Volmer reaction and negative potentials induced Mo2O72- (from MoO42-) further enhances proton adsorption and H2 desorption. Leveraging these insights, the well-designed MoO42-/Mo2O72- modified Co(OH)2@Co2Mo3O8 catalyst achieves a Faradaic efficiency of 99.9% and a yield of 1.85 mol h-1 at -0.4 V versus reversible hydrogen electrode (RHE) for hydrogen generation. Moreover, it maintains stable over one month at approximately 100 mA cm-2, highlighting its industrial suitability. This work underscores the significance of understanding on precatalyst reconstruction and electrolyte evolution in catalyst design.

The Spin-Selective Channels in Fully-Exposed PtFe Clusters Enable Fast Cathodic Kinetics of Li-O2 Battery

In Li-O2 batteries (LOBs), the electron transfer between triplet O2 and singlet Li2O2 possesses a spin-dependent character but is still neglected, while the spin-conserved electron transfer without losing phase information should guarantee fast kinetics and reduced energy barriers. Here, we provide a paradigm of spin-selective catalysis for LOB that the ferromagnetic quantum spin exchange interactions between Pt and Fe atoms in fully-exposed PtFe clusters filter directional e-spins for spin-conserved electron transfer at Fe-Fe sites. The kinetics of O2/Li2O2 redox reaction is markedly accelerated as predicted by theoretical calculations, showing dramatically decreased relaxation time of the rate determining step for more than one order of magnitude, compared with the Fe clusters without spin-selective behavior. In consequence, the assembled LOB provides ultrahigh energy conversion efficiency of 89.6 % at 100 mA g-1 under a discharge-charge overpotential of only 0.32 V. This work provides new insights into the spin-dependent mechanisms of O2/Li2O2 redox reaction, and the strategy of constructing spin catalysts at atomic level.

Valence Electron: A Descriptor of Spinel Sulfides for Sulfur Reduction Catalysis

Catalysts are essential for achieving high-performance lithium-sulfur batteries. The precise design and regulation of catalytic sites to strengthen their efficiency and robustness remains challenging. In this study, spinel sulfides and catalyst design principles through element doping are investigated. This research highlights the distinct role of lattice sulfur sites in lithium polysulfide conversion and emphasizes the differences in catalytic activity between metal and anion sites. The valence electron model as a descriptor can characterize catalytic performance, guiding the design of a (FeCo)3(PS)4 catalyst co-doped with cation and anion. The (FeCo)3(PS)4 exhibits the highest catalytic performance among spinel catalysts to data, particularly under high sulfur loading conditions. It achieves an initial specific capacity of 1205.9 mAh g-1 (6.1 mAh cm-2) at a sulfur loading of 5 mg cm-2 and 1192.7 mAh g-1 (11.9 mAh cm-2) at 10 mg cm-2, demonstrating excellent electrocatalytic performance.

Real-Time Detection of Dynamic Restructuring in KNixFe1- xF3 Perovskite Fluorides for Enhanced Water Oxidation

Mechanistic understanding of how electrode-electrolyte interfaces evolve dynamically is crucial for advancing water-electrolysis technology, especially the restructuring of catalyst surface during complex electrocatalytic reactions. However, for perovskite fluorides, the mechanistic exploration for the influence of the dynamic restructuring on their chemical property and catalytic mechanism is unclear due to their poor conductivity that makes the definition of electrocatalyst structure difficult. Herein, for oxygen evolution reaction (OER), various operando characterizations are employed to investigate the structure-activity relationships of the KNixFe1- xF3@NF. Adding iron to the KNixFe1- xF3 structure increases metal vacancies, enhancing electrochemical reconstruction. For reconstructed KNixFe1- xF3 structure, the results from operando Raman, operando X-ray diffraction, operando UV-vis spectroscopy, and differential electrochemical mass spectrometry reveal that the surface Ni sites act as catalytic centers within the amorphous Ni(Fe)OOH active layer, and the incorporation of Fe activates oxidized oxygen ions during water oxidation. Theoretical calculations support this by demonstrating the optimized adsorption-free energy of oxygenated intermediates. Consequently, the KNi0.5Fe0.5F3@NF achieves an overpotential of 281 mV to reach OER current of 150 mA·cm-2 and maintains stable operation for 200 h. These results highlight a promising pathway to tuning OER mechanisms in perovskite fluorides and offer a new perspective for developing high-efficiency and durable OER catalysts.

Creating Spin Channels in SrCoO3 through Trigonal-to-Cubic Structural Transformation for Enhanced Oxygen Evolution/Reduction Reactions

Oxygen evolution and reduction reactions (OER and ORR) play crucial roles in energy conversion processes such as water splitting and air batteries, where spin dynamics inherently influence their efficiency. However, the specific contribution of spin has yet to be fully understood. In this study, we intentionally introduce a spin channel through the transformation of trigonal antiferromagnetic SrCoO2.5 into cubic ferromagnetic SrCoO3, aiming to deepen our understanding of spin dynamics in catalytic reactions. Based on the results from spherical-aberration-corrected microscopy, synchrotron absorption spectra, magnetic characterizations, and density functional theory calculations, it is revealed that surface electron transfer is predominantly governed by local geometric structures, while the presence of the spin channel significantly enhances the bulk transport of spin-polarized electrons, particularly under high current densities where surface electron transfer is no longer the limiting factor. The overpotential for OER is reduced by at least 70 mV at 150 mA cm-2 due to the enhanced conductivity from spin-polarized electrons facilitated by spin channels, with an expectation of even more significant reductions at higher current densities. This work provides a clearer picture of the role of spin in oxygen-involved electrocatalysis, providing critical insights for the design of more efficient catalytic systems in practical applications.

Improved Catalyst Performance for the Oxygen Evolution Reaction under a Chiral Bias

The oxygen evolution reaction (OER) remains an important bottleneck for widespread implementation of a hydrogen economy. While improvements in the OER can be realized by spin polarizing the reaction intermediates, these methods often rely on applying external magnetic fields to ferromagnetic catalysts or by adsorbing chiral molecules onto the catalyst. Here, we show that the addition of chiral additives to the conductive binder supporting the catalysts enhances the selectivity for O2 formation and results in exceedingly high mass activities. The results are explained within the context of a statistical model in which the additives are hypothesized to act as a localized chiral bias that enhances radical intermediate coupling. More broadly, these studies illustrate a flexible design motif for improving OER catalysis that persists under different pH conditions, is independent of the choice of catalyst, and can be extrapolated to other chemical reactions.

Quantum fundaments of catalysis: true electronic potential energy

Catalysis is a quantum phenomenon enthalpically driven by electronic correlations with many-particle effects in all of its branches, including electro-photo-catalysis and electron transfer. This means that only probability amplitudes provide a complete relationship between the state of catalysis and observations. Thus, in any atomic system material), competing space-time electronic interactions coexist to define its (related) properties such as stability, (super)conductivity, magnetism (spin-orbital ordering), chemisorption and catalysis. Catalysts, reactants, and chemisorbed and transition states have the possibility of optimizing quantum correlations to improve reaction kinetics. Active sites with closed-shell orbital configurations share a maximum number of spin-paired electrons, mainly optimizing coulombic attractions and covalency and defining weakly correlated closed-shell (WCCS) structures. However, in compositions with open-shell orbital configurations, at least, quantum spin exchange interactions (QSEIopenshells) arise, stabilising unpaired electrons in less covalent bonds and differentiating non-weakly (or strongly) correlated open-shell (NWCOS) systems. In NWCOS catalysts, electronic ground states can have bonds with diverse and rival spin-orbital orderings as well as ferro-, ferri- and multiple antiferro-magnetic textures, which deeply define their activities. Particularly in inter-atomic ferromagnetic (FM) bonds, the increase in relevance of non-classical quantum potentials can significantly optimize chemisorption energies, transition states (TSs), activation energies (overpotential) and spin-dependent electron transfer (conductivity), overall implying the need for explaining the thermodynamic and kinetic origin of catalysis from its true quantum electronic energy. To do so, we use the connection between the Born-Oppenheimer approximation and Virial theorem in the treatment of electronic kinetic and potential energies. Thus, the exact fundamental interactions that decompose TSs appear. The possibility of increasing the stabilization of TSs, due to quantum correlations on NWCO catalysts, opens the possibility of simultaneously reducing chemisorption enthalpies and activation barriers of reaction mechanisms, which implies the anticipation and explanation of positive deviations from the Brønsted-Evans-Polanyi principle.

Silver Nanowires Cascaded Layered Double Hydroxides Nanocages with Enhanced Directional Electron Transport for Efficient Electrocatalytic Oxygen Evolution

Designing and fabricating highly efficient oxygen evolution reaction (OER) electrocatalytic materials for water splitting is a promising and practical approach to green and sustainable low-carbon energy systems. Herein, a facile in situ growth self-template strategy by using ZIF-67 as a consumable layered double hydroxides (LDHs) template and silver nanowires (AgNWs) as 1D conductive cascaded substrate to controllably synthesize the target AgNWs@CoFe-LDH composites with unique hollow shell sugar gourd-like structure and enhanced directional electron transport effect is reported. The AgNWs exhibit the key functions of the close connection of CoFe-LDH nanocages and the support of the directional electron transport effect in the composite catalyst inducing electrons directionally moving from CoFe-LDH to AgNWs. Meanwhile, the CoFe-LDH nanocages with ultrathin nanosheets and hollow structural properties show abundant active sites for electrocatalytic oxygen generation. The versatile AgNWs@CoFe-LDH catalyst with optimized components, enhanced directional electron transport, and synergistic effect achieves high OER performance with the overpotential of 207 mV and long-term 50 h stability at 10 mA cm-2 in an alkaline medium. Moreover, in-depth insights into the microstructure, structure-activity relationships, identification of key intermediate species, and a proton-coupled four-electron OER mechanism based on experimental discovery and theoretical calculation are also demonstrated.

Enhancing the electronic structure of Ni-based electrocatalysts through N element substitution for the hydrogen evolution reaction

The weak orbital coupling between Ni3N and H2O, caused by its interstitial structure and attenuated Ni-N interaction, is attributed to the high unoccupied d orbital energy of Ni3N. Consequently, the kinetics for water dissociation in the HER are slow. In this study, we effectively lowered the energy state of vacant d orbitals in Ni3N, which resulted in an exceptionally efficient HER. The as-synthesized Ni3N catalyst demonstrates an overpotential of 135 mV when subjected to a current density of 10 mA cm-2. The refined structural characterization suggests that the introduction of oxygen results in a reduction in electron densities surrounding the Ni sites. Furthermore, DFT calculations provide additional evidence that the electrocatalyst of Ni3N generates a greater number of lowest unoccupied orbitals (LUMOs) and improved alignment, thereby enhancing the adsorption and splitting of water. The notion of orbital-regulated electronic levels on Ni sites introduces a distinctive methodology for the systematic development of catalysts used in hydrogen evolution and other applications.

Bifunctional Electrocatalysts for Overall and Hybrid Water Splitting

Electrocatalytic water splitting driven by renewable electricity has been recognized as a promising approach for green hydrogen production. Different from conventional strategies in developing electrocatalysts for the two half-reactions of water splitting (e.g., the hydrogen and oxygen evolution reactions, HER and OER) separately, there has been a growing interest in designing and developing bifunctional electrocatalysts, which are able to catalyze both the HER and OER. In addition, considering the high overpotentials required for OER while limited value of the produced oxygen, there is another rapidly growing interest in exploring alternative oxidation reactions to replace OER for hybrid water splitting toward energy-efficient hydrogen generation. This Review begins with an introduction on the fundamental aspects of water splitting, followed by a thorough discussion on various physicochemical characterization techniques that are frequently employed in probing the active sites, with an emphasis on the reconstruction of bifunctional electrocatalysts during redox electrolysis. The design, synthesis, and performance of diverse bifunctional electrocatalysts based on noble metals, nonprecious metals, and metal-free nanocarbons, for overall water splitting in acidic and alkaline electrolytes, are thoroughly summarized and compared. Next, their application toward hybrid water splitting is also presented, wherein the alternative anodic reactions include sacrificing agents oxidation, pollutants oxidative degradation, and organics oxidative upgrading. Finally, a concise statement on the current challenges and future opportunities of bifunctional electrocatalysts for both overall and hybrid water splitting is presented in the hope of guiding future endeavors in the quest for energy-efficient and sustainable green hydrogen production.

Surface reconstruction of pyrite-type transition metal sulfides during oxygen evolution reaction

Reconstruction universally occurs over non-layered transition metal sulfides (TMSs) during oxygen evolution reaction (OER), leading to the formation of active species metal (oxy)hydroxide and thus significantly influences the OER performance. However, the reconstruction process and underlying mechanism quantitatively remain largely unexplored. Herein, we proposed an electrochemical reaction mechanism, namely sulfide oxidation reaction (SOR), to elucidate the reconstruction process of pyrite-type TMSs. Based on this mechanism, we evaluated the reconstruction capability of NiS2 doped with transition metals V, Cr, Mn, Fe, Co, Cu, Mo, Ru, Rh, and Ir within different doped systems. Two key descriptors were thus proposed to describe the reconstruction abilities of TMSs: USOR (the theoretical electric potential of SOR) and ΔU (the difference between the theoretical electric potential of SOR and OER), representing the initiation electric potential of reconstruction and the intrinsic reconstruction abilities of TMSs, respectively. Our finding shows that a lower USOR readily initiate reconstruction at a lower potential and a larger ΔU indicating a poorer reconstruction ability of the catalyst during OER. Furthermore, Fe-doped CoS2 was used to validate the rationality of our proposed descriptors, being consistent with the experiment findings. Our work provides a new perspective on understanding the reconstruction mechanism and quantifying the reconstruction of TMSs.

Manipulation of Electron Spins with Oxygen Vacancy on Amorphous/Crystalline Composite-Type Catalyst

By substituting the oxygen evolution reaction (OER) with the anodic urea oxidation reaction (UOR), it not only reduces energy consumption for green hydrogen generation but also allows purification of urea-rich wastewater. Spin engineering of the d orbital and oxygen-containing adsorbates has been recognized as an effective pathway for enhancing the performance of electrocatalysts. In this work, we report the fabrication of a bifunctional electrocatalyst composed of amorphous RuO2-coated NiO ultrathin nanosheets (a-RuO2/NiO) with abundant amorphous/crystalline interfaces for hydrogen evolution reaction (HER) and UOR. Impressively, only 1.372 V of voltage is required to attain a current density of 10 mA cm-2 over a urea electrolyzer. The increased oxygen vacancies in a-RuO2/NiO by incorporation of amorphous RuO2 enhance the total magnetization and entail numerous spin-polarized electrons during the reaction, which speeds up the UOR reaction kinetics. The density functional theory study reveals that the amorphous/crystalline interfaces promote charge-carrier transfer, and the tailored d-band center endows the optimized adsorption of oxygen-generated intermediates. This kind of oxygen vacancy induced spin-polarized electrons toward boosting HER and UOR kinetics and provides a reliable reference for exploration of advanced electrocatalysts.

Thermal suppression of charge disproportionation accelerates interface electron transfer of water electrolysis

The sluggish electron transfer kinetics in electrode polarization driven oxygen evolution reaction (OER) result in big energy barriers of water electrolysis. Accelerating the electron transfer at the electrolyte/catalytic layer/catalyst bulk interfaces is an efficient way to improve electricity-to-hydrogen efficiency. Herein, the electron transfer at the Sr3Fe2O7@SrFeOOH bulk/catalytic layer interface is accelerated by heating to eliminate charge disproportionation from Fe4+ to Fe3+ and Fe5+ in Sr3Fe2O7, a physical effect to thermally stabilize high-spin Fe4+ (t2g3eg1), providing available orbitals as electron transfer channels without pairing energy. As a result of thermal-induced changes in electronic states via thermal comproportionation, a sudden increase in OER performances was achieved as heating to completely suppress charge disproportionation, breaking a linear Arrhenius relationship. The strategy of regulating electronic states by thermal field opens a broad avenue to overcome the electron transfer barriers in water splitting.

Improving Electrocatalytic Oxygen Evolution through Local Field Distortion in Mg/Fe Dual-site Catalysts

Transition metal single atom electrocatalysts (SACs) with metal-nitrogen-carbon (M-N-C) configuration show great potential in oxygen evolution reaction (OER), whereby the spin-dependent electrons must be allowed to transfer along reactants (OH- /H2 O, singlet spin state) and products (O2 , triplet spin state). Therefore, it is imperative to modulate the spin configuration in M-N-C to enhance the spin-sensitive OER energetics, which however remains a significant challenge. Herein, we report a local field distortion induced intermediate to low spin transition by introducing a main-group element (Mg) into the Fe-N-C architecture, and decode the underlying origin of the enhanced OER activity. We unveil that, the large ionic radii mismatch between Mg2+ and Fe2+ can cause a FeN4 in-plane square local field deformation, which triggers a favorable spin transition of Fe2+ from intermediate (dxy 2 dxz 2 dyz 1 dz2 1 , 2.96 μB ) to low spin (dxy 2 dxz 2 dyz 2 , 0.95 μB ), and consequently regulate the thermodyna-mics of the elementary step with desired Gibbs free energies. The as-obtained Mg/Fe dual-site catalyst demonstrates a superior OER activity with an overpotential of 224 mV at 10 mA cm-2 and an electrolysis voltage of only 1.542 V at 10 mA cm-2 in the overall water splitting, which outperforms those of the state-of-the-art transition metal SACs.

Interface Engineering a High Content of Co3+ Sites on Co3O4 Nanoparticles to Boost Acidic Oxygen Evolution

Non-noble metal oxides have emerged as potential candidate electrocatalysts for acidic oxygen evolution reactions (OERs) due to their earth abundance; however, improving their catalytic activity and stability simultaneously in strong acidic electrolytes is still a major challenge. In this work, we report Co3O4@carbon core-shell nanoparticles on 2D graphite sheets (Co3O4@C-GS) as mixed-dimensional hybrid electrocatalysts for acidic OER. The obtained Co3O4@C-GS catalyst exhibits a low overpotential of 350 mV and maintains stability for 20 h at a current density of 10 mA cm-2 in H2SO4 (pH = 1) electrolyte. X-ray photoelectron and X-ray absorption spectroscopies illustrate that the higher content of Co3+ sites boosts acidic OER. Operando Raman spectroscopy reveals that the catalytic stability of Co3O4@C nanoparticles during the acidic OER is enhanced by the introduction of graphite sheets. This interface engineering of non-noble metal sites with high valence states provides an efficient approach to boost the catalytic activity and enhance the stability of noble-metal-free electrocatalysts for acidic OER.

A Perspective of Magnetoelectric Effect in Electrocatalysis

The integration of magnetic fields with magnetoelectric (ME) coupling materials has been recently reported for electrocatalysis applications. Highly efficient energy conversion and storage can be potentially provided by this emerging approach. The ME properties, that is, the coexistence of ferromagnetic (FM) and ferroelectric (FE) ordering in some multiferroic materials, can be manipulated by magnetic or electric fields. The ME coupling can result in unique spin-related physical properties in catalysts, further leading to interesting effects on electrocatalytic reactions. Herein, a discussion on the ME coupling multiferroic materials, as well as their potential opportunities and challenges as electrocatalysts in selected electrochemical reactions, is provided.

Hetero-Anionic Structure Activated CoS Bonds Promote Oxygen Electrocatalytic Activity for High-Efficiency Zinc-Air Batteries

The electronic structure of transition metal complexes can be modulated by replacing partial ion of complexes to obtain tuned intrinsic oxygen reduction reaction (ORR) or oxygen evolution reaction (OER) electrocatalytic activity. However, the anion-modulated transition metal complexes ORR activity of is still unsatisfactory, and the construction of hetero-anionic structure remains challenging. Herein, an atomic doping strategy is presented to prepare the CuCo2 O4-x Sx /NC-2 (CCSO/NC-2) as electrocatalysts, the structrual characterization results favorably demonstrate the partial substitution of S atoms for O in CCSO/NC-2, which shows excellent catalytic performance and durability for OER and ORR in 0.1 m KOH. In addition, the catalyst assembled Zinc-air battery with an open circuit potential of 1.43 V maintains performance after 300 h of cyclic stability. Theoretical calculations and differential charges illustrate that S doping optimizes the reaction kinetics and promotes electron redistribution. The superior performance of CCSO/NC-2 catalysis is mainly due to its unique S modulation of the electronic structure of the main body. The introduction of S promotes CoO covalency and constructs a fast electron transport channel, thus optimizing the adsorption degree of active site Co to the reaction intermediates.

Rational Design of Cu-Doped Tetrahedron of Spinel Oxide for High-Performance Nitric Oxide Electrochemical Sensor

The real-time detection of nitric oxide (NO) in living cells is essential to reveal its physiological processes. However, the popular electrochemical detection strategy is limited to the utilization of noble metals. The development of new detection candidates without noble metal species still maintaining excellent catalytic performance has become a big challenge. Herein, we propose a spinel oxide doped with heteroatom-Cu-doped Co₃O₄ (Cu-Co₃O₄) for the sensitive and selective detection of NO release from the living cells. The material is strategically designed with Cu occupying the tetrahedral (T_d) center of Co₃O₄ through the formation of a Cu-O bond. The introduced Cu regulates the local coordination environment and optimizes the electronic structure of Co₃O₄, hybridizing with the N 2p orbital to enhance charge transfer. The Cu_Td site can well inhibit the current response to nitrite (NO₂^-), resulting in a high improvement in the electrochemical oxidation of NO. The selectivity of Cu-Co₃O₄ can be markedly improved by the pore size of the molecular sieve and the negative charge on the surface. The rapid transmission of electrons is due to the fact that Cu-Co₃O₄ can be uniformly and densely in situ grown on Ti foil. The rationally designed Cu-Co₃O₄ sensor displays excellent catalytic activity toward NO oxidation with a low limit of detection of 2.0 nM (S/N = 3) and high sensitivity of 1.9 μA nM^-1 cm^-2 in cell culture medium. The Cu-Co₃O₄ sensor also shows good biocompatibility to monitor the real-time NO release from living cells (human umbilical vein endothelial cells: HUVECs; macrophage: RAW 264.7 cells). It was found that a remarkable response to NO was obtained in different living cells when stimulated by l-arginine (l-Arg). Moreover, the developed biosensor could be used for real-time monitoring of NO released from macrophages polarized to a M1/M2 phenotype. This cheap and convenient doping strategy shows universality and can be used for sensor design of other Cu-doped transition metal materials. The Cu-Co₃O₄ sensor presents an excellent example through the design of proper materials to implement unique sensing requirements and sheds light on the promising strategy for electrochemical sensor fabrication.

Amorphous Oxysulfide Reconstructed from Spinel NiCo2 S4 for Efficient Water Oxidation

The progress of effective and durable electrocatalysts for oxygen evolution reaction (OER) is urgent, which is essential to promote the overall efficiency of green hydrogen production. To improve the performance of spinel cobalt-based oxides, which serve as promising water oxidation electrocatalysts in alkaline electrolytes, most researches have been concentrated on cations modification. Here, an anionic regulation mechanism is employed to adopt sulfur(S) anion substitution to supplant NiCo₂ O₄ by NiCo₂ S₄ , which contributed to an impressive OER performance in alkali. It is revealed that the substitution of S constructs a sub-stable spinel structure that facilitates its reconstruction into active amorphous oxysulfide under OER conditions. More importantly, as the active phase in the actual reaction process, the hetero-anionic amorphous oxysulfide has an appropriately tuned electronic structure and efficient OER electrocatalytic activity. This work demonstrates a promising approach for achieving anion conditioning-based tunable structure reconstruction for robust and easy preparation spinel oxide OER electrocatalysts.

Defect engineering of two-dimensional materials for advanced energy conversion and storage

In the global trend towards carbon neutrality, sustainable energy conversion and storage technologies are of vital significance to tackle the energy crisis and climate change. However, traditional electrode materials gradually reach their property limits. Two-dimensional (2D) materials featuring large aspect ratios and tunable surface properties exhibit tremendous potential for improving the performance of energy conversion and storage devices. To rationally control the physical and chemical properties for specific applications, defect engineering of 2D materials has been investigated extensively, and is becoming a versatile strategy to promote the electrode reaction kinetics. Simultaneously, exploring the in-depth mechanisms underlying defect action in electrode reactions is crucial to provide profound insight into structure tailoring and property optimization. In this review, we highlight the cutting-edge advances in defect engineering in 2D materials as well as their considerable effects in energy-related applications. Moreover, the confronting challenges and promising directions are discussed for the development of advanced energy conversion and storage systems.