Electronic redistribution induced by interaction between ruthenium nanoparticles and Ni-N(O)-C sites boosts alkaline water electrolysis

Selective electrooxidation of 5-hydroxymethylfurfural to value-added 2,5-furanodiformic acid: mechanism, electrolyzer system, and electrocatalyst regulation

Value-added chemical products derived from biomass have attracted wide attention in addressing global warming and fossil fuel pollution. Among them, 2,5-furanodiformic acid (FDCA), the oxidized product of 5-hydroxymethylfurfural (HMF), is an effective substitute for terylene acid extracted from petroleum to synthesize biodegradable plastics. Electrochemical oxidation is an environmentally friendly, mild reaction condition, high-efficiency process for converting HMF to FDCA. However, the electrooxidation of HMF involves six-electron transfer, normally leading to the formation of many by-products. Thus, there is still a need to construct highly selective catalysts for HMF electrooxidation to FDCA. In this review, first we have investigated the mechanism of HMF electrooxidation and summarized the electrolytic cells and product analysis methods for electrooxidation of HMF to FDCA. The factors influencing HMF electrooxidation to FDCA are also discussed. Then, the electronic structure regulation methods of various electrocatalysts including heteroatom doping, heterostructure construction, interfacial engineering, and defect engineering are systematically summarized for the highly selective electrooxidation of HMF to FDCA. Finally, future challenges and prospects are proposed for further deep understanding. It is expected that this review could provide new guidance for large-scale electrooxidation of HMF to FDCA in industry.

Constructing nanoneedle arrays of heterostructured RuO2-Co3O4 with tip-effect-induced enrichment of reactants for enhanced water oxidation

Nanoneedle arrays of heterostructured RuO2-Co3O4 electrocatalysts were constructed, showing improved water oxidation activity and durable stability. The synergy of tip-effect-induced OH- enrichment, superior hydrophilicity, and heterojunction-enhanced electron transfer promotes water oxidation activity.

Anti-Sintering Ni-W Catalytic Layer on Reductive Tungsten Carbides for Superior High-Temperature CO2 Reduction

The reverse water-gas shift (RWGS) reaction stands out as a promising approach for selectively converting CO2 into CO, which can then be upgraded into high-value-added products. While designing high selectivity and stability catalysts for RWGS reaction remains a significant challenge. In this study, an efficient and ultra-stable Ni-W catalytic layer on reductive WC (NiAWC) is designed as an anti-sintering catalyst for superior high-temperature RWGS reaction. Benefiting from the unique structures, the NiAWC catalyst exhibits exceptionally high performances with a CO production rate of 1.84 molCO gNi -1 h-1 and over 95% CO selectivity, maintaining stability for 120 h at 500 °C. Even after 300 h of continuous testing at 600 °C and five aging cycles at 800 °C, the activity loss is only 0.34% and 0.83%, respectively. Unlike the conventional mechanism in RWGS reaction, it is demonstrated that the Ni-W limited coordination can stabilize the Ni sites and allow a pre-oxidation of Niδ+ by CO, which produces an O* electronic reservoir and hinders the charge transfer from Ni to W-O, thereby avoiding the dissolution of Ni atoms. The design of new, efficient, and selective catalysts through metal-substrate synergistic effects is suggested to offer a promising path to engineering superior thermal catalysts.

Harnessing Spin-Lattice Interplay in Metal Nitrides for Efficient Ammonia Electrosynthesis

Metal nitrides, renowned for their spin-lattice-charge interplay, offer vast potential in catalysis, electronics, and energy conversion. However, spin polarization manipulation in these nitrides remains a challenge for multi-electron electrocatalytic processes. This study introduces Co3Mo3N with a low-spin polarization configuration, achieved by incorporating spin-free lattice Mo with 4d orbitals into high-spin polarization Co4N. This innovation delivers outstanding nitrate-to-ammonia electrosynthesis, ranking among the best to date. Mo inclusion induces competing magnetic exchange interactions, reducing the spin polarization degree and enabling rate-determining step of NO2* to NO-OH* conversion via vertex-sharing NMo6 octahedra. A paired electro-refinery with a Co3Mo3N cathode achieves 2 000 mA cm-2 at 2.28 V and sustains an industrial-scale current of 1 000 mA cm-2 for 2,100 h, with an NH3 production rate of ≈70 mg NH3 h-1 cm-2. This work establishes a transformative platform for spin polarization degree-engineered electrocatalysts, driving breakthroughs in energy conversion technologies.

Impact of harmful ions in seawater on electrolysis catalysts: challenges and mitigation strategies

Direct seawater electrolysis presents a promising solution to address both freshwater scarcity and the growing demand for green hydrogen in regions abundant in renewable energy. This study first investigates the electrochemical mechanisms of seawater electrolysis, decomposing the process into cathodic and anodic reactions. It then reviews the impact of seawater's complex ionic composition on electrocatalyst performance, focusing on activity, selectivity, and stability. The challenges posed by anionic interference from Cl- and Br-, and cationic interference from Mg2+ and Ca2+, are discussed, along with effective mitigation strategies. Solutions to mitigate the impact of anions on the anode, such as heterojunction engineering, nanostructure design and constructing anti-corrosion layers, are proposed. Anodic small molecule oxidation is employed as an alternative to the oxygen evolution reaction (OER) to decrease the overall energy consumption. For the cationic interference on the cathode, strategies like maintaining the hydrophobicity of the electrode and electrolysis cell design are suggested. Finally, this review summarizes the remaining challenges, presents feasible solutions, and highlights key considerations for scaling up seawater electrolysis for commercial hydrogen production. This review provides valuable insights to accelerate the development of sustainable, large-scale seawater hydrogen production technologies.

Highly Active NiRu/C Cathode Catalyst Synthesized by Displacement Reaction for Anion Exchange Membrane Water Electrolysis

Anion exchange membrane water electrolysis (AEMWE) is highly promising for cost-effective green hydrogen production due to its basic operating conditions facilitating the use of non-noble catalysts. While non-noble Ni/Fe-based catalysts are utilized at the anode, its cathode catalyst still requires precious Pt. Due to the high cost of Pt and the sluggish hydrogen evolution reaction (HER) at the cathode in basic conditions, developing alternative catalysts to replace Pt is highly important. Here, a synthesis procedure for a Ru-based catalyst is reported and its high activity toward the HER in alkaline media is demonstrated in both half-cell and single-cell tests. The catalyst is synthesized in a two-step approach. A highly dispersed Ni catalyst is prepared on carbon support in the first step. In the second step, Ru is deposited on its surface using a galvanic displacement reaction. The uniqueness of this method is that Ru is deposited over the entire electrically conductive surface, resulting in an isotropic and homogeneous Ru distribution within the catalyst powder. It is demonstrated that this material remarkably outperforms state-of-the-art Pt/C catalysts in half-cell and single-cell tests. The single cell only requires 1.73 V at 1 A cm-2 with an overall PGM content of 0.05 mg cm-2.

Industrial-current Ammonia Synthesis by Polarized Cuprous Cyanamide Coupled to Valorization of Glycerol at 4,000 mA cm-2

The electrocatalytic nitrate reduction (NO3RR) holds significance in both NH3 synthesis and nitrate contamination remediation. However, achieving industrial-scale current and high stability in membrane electrode assembly (MEA) electrolyzer remains challenging due to inherent high full-cell voltage for sluggish NO3RR and water oxidation. Here, Cu2NCN with positive surface electrostatic potential VS(r) is applied as highly efficient NO3RR electrocatalysts to achieve industrial-current and low-voltage stable NH3 production in MEA electrolyzer with coupled anodic glycerol oxidation. This paired electro-refinery (PER) system reaches 4000 mA cm-2 at 2.52 V and remains stable at industrial-level 1000 mA cm-2 for 100 h with the NH3 production rate of 97000 µgNH3 h-1 cm-2 and a Faradaic efficiency of 83%. Theoretical calculations elucidate that the asymmetric and electron-withdrawing [N-C≡N] units enhance polarization and VS(r), promoting robust and asymmetric adsorption of NO3 * on Cu2NCN to facilitate O-N bond dissociation. A comprehensive techno-economic analysis demonstrates the profitability and commercial viability of this coupled system. Our work opens a new avenue and marks a significant advancement in MEA systems for industrial NH3 synthesis.

Electrochemical Lithiation Regulates the Active Hydrogen Supply on Ru-Sn Nanowires for Hydrogen Evolution Toward the High-Performing Anion Exchange Membrane Water Electrolyzer

Designing a rational electrocatalyst/electrolyte interface with superb active hydrogen supply is of significant importance for the alkaline hydrogen evolution reaction (HER) and anion exchange membrane water electrolyzers (AEMWEs). Here, we propose a strategy to tune the interfacial active hydrogen supply via inducing dissoluble cation into electrocatalysts to boost HER in alkali, with electrochemical lithiated sub-2 nm RuSn0.8 nanowires (NWs) as a proof of concept. It is found that a part of Li+ could dissolve in situ from lithiated RuSn0.8 NWs during HER, which tends to affect the interfacial structure and facilitate the proton transport. Among all the Li-Ru-Sn and Ru-Sn NWs, the best-performing Li3.0RuSn0.8 NWs exhibit the lowest initial overpotential of 66 mV at 100 mA cm-2 in 1.0 M KOH, which could be further reduced to 38 mV after the 30 000 cycles accelerated stability test (AST). In situ Raman spectroscopy and operando X-ray adsorption spectroscopy indicate that the pristine Li3.0RuSn0.8 NWs are highly active toward water dissociation and the dissolved Li+ during AST could further enhance the flexibility of the hydrogen bond network for proton transportation. Ab initio molecular dynamics simulations and density functional theory calculations disclose that the incorporation of Li into the Ru-Sn lattice is beneficial to lower the water dissociation barrier, while dissolved Li+ at the interface significantly increases the population of interfacial water molecules, thereby providing sufficient active hydrogens for H2 production. The AEMWE equipped with the Li3.0RuSn0.8 NWs cathode delivers an extremely low cell voltage (1.689 V) at an industrial-scale current density (1 A cm-2) and outstanding stability (56 μV h-1 loss at 1 A cm-2 after 1000 h galvanostatic test), representing one of the best alkaline HER electrocatalysts ever reported.

A Copper-Zinc Cyanamide Solid-Solution Catalyst with Tailored Surface Electrostatic Potentials Promotes Asymmetric N-Intermediate Adsorption in Nitrite Electroreduction

The electrocatalytic nitrite reduction (NO2RR) converts nitrogen-containing pollutants to high-value ammonia (NH3) under ambient conditions. However, its multiple intermediates and multielectron coupled proton transfer process lead to low activity and NH3 selectivity for the existing electrocatalysts. Herein, we synthesize a solid-solution copper-zinc cyanamide (Cu0.8Zn0.2NCN) with localized structure distortion and tailored surface electrostatic potential, allowing for the asymmetric binding of NO2-. It exhibits outstanding NO2RR performance with a Faradaic efficiency of ∼100% and an NH3 yield of 22 mg h-1 cm-2, among the best for such a process. Theoretical calculations and in situ spectroscopic measurements demonstrate that Cu-Zn sites coordinated with linear polarized [NCN]2- could transform symmetric [Cu-O-N-O-Cu] in CuNCN-NO2- to a [Cu-N-O-Zn] asymmetric configuration in Cu0.8Zn0.2NCN-NO2-, thus enhancing adsorption and bond cleavage. A paired electro-refinery with the Cu0.8Zn0.2NCN cathode reaches 2000 mA cm-2 at 2.36 V and remains fully operational at industrial-level 400 mA cm-2 for >140 h with a NH3 production rate of ∼30 mgNH3 h-1 cm-2. Our work opens a new avenue of tailoring surface electrostatic potentials using a solid-solution strategy for advanced electrocatalysis.

Engineering the Sandwich-Type Porphyrinic MOF-Ruthenium-Nickel Foam Electrode for Boosting Overall Water Splitting via Self-Reconstruction

The rational construction of a hierarchical noble metal-metal-organic frameworks (MOFs) structure is anticipated to yield enduring and highly efficient performance in alkaline electrocatalytic water splitting. Herein, a sandwich construction strategy is employed to enhance the stability, wherein active RutheniRu (Ru) nanosheets are incorporated onto nickel foam (NF) and subsequently covered with porphyrinic MOFs (PMOFs). In addition, activated PMOF-NiOOH-Ru20/NF-C/A electrodes are obtained by electrochemical self-reconstruction as cathode and anode, respectively. Density functional theory (DFT) calculations demonstrated that the resulting PMOF-NiOOH-Ru heterointerface effectively facilitated electron transfer, enhanced H2O adsorption capacity, and optimized ΔG values for *H and *O to *OOH. Consequently, PMOF-NiOOH-Ru20/NF-C/A exhibited low overpotentials for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), accompanied by minimal Ru leakage. Furthermore, stable overall water splitting can be achieved with a low voltage of 1.456 V@10 mA cm-2 for over 120 h. Even when operated in simulated seawater, the prepared electrodes demonstrated similar activity and stability. This study contributes to a deeper understanding of the regulation mechanism for the performance and stability of active sites in the electrocatalytic self-reconstruction process.

TiN Boosting the Oxygen Reduction Performance of Fe-N-C through the Relay-Catalyzing Mechanism for Metal-Air Batteries

Metal-air batteries desire highly active, durable, and low-cost oxygen reduction catalysts to replace expensive platinum (Pt). The Fe-N-C catalyst is recognized as the most promising candidate for Pt; however, its durability is hindered by carbon corrosion, while activity is restricted due to limited oxygen for the reaction. Herein, TiN is creatively designed to be hybridized with Fe-N-C (TiN/Fe-N-C) to relieve carbon corrosion and absorb more oxygen when catalyzing oxygen reduction. The half-wave potential of TiN/Fe-N-C is 0.915 V vs reverse hydrogen electrode with 15 mV lost after 30,000 cycles accelerated durability test, higher than 0.893 V and 26 mV of Pt/C. The solid zinc-air battery of TiN/Fe-N-C achieves a peak power density of 238 mW/cm2, 2100 cycle stability at 30 °C, and long-term durability of 1100 h under -20 °C, superior to 150 mW/cm2 and 500 h (-20 °C) of Pt/C. Both calculations and experiments indicate that TiN has dual functions which not only relay abundant oxygen for the reaction but also strengthen the adsorption force for intermediates of carbon corrosion reaction, thus, enhancing the activity and durability of Fe-N-C. Therefore, the proposed relay catalytic strategy by TiN offers an efficient Fe-N-C catalyst for energy conversion devices.

Near-Unity Photothermal CO2 Hydrogenation to Methanol Based on a Molecule/Nanocarbon Hybrid Catalyst

Solar-driven CO2-to-methanol conversion provides an intriguing route for both solar energy storage and CO2 mitigation. For scalable applications, near-unity methanol selectivity is highly desirable to reduce the energy and cost endowed by low-value byproducts and complex separation processes, but so far has not been achieved. Here we demonstrate a molecule/nanocarbon hybrid catalyst composed of carbon nanotube-supported molecularly dispersed cobalt phthalocyanine (CoPc/CNT), which synergistically integrates high photothermal conversion capability for affording an optimal reaction temperature with homogeneous and intrinsically-efficient active sites, to achieve a catalytic activity of 2.4 mmol gcat -1 h-1 and selectivity of ~99 % in direct photothermal CO2 hydrogenation to methanol reaction. Both theoretical calculations and operando characterizations consistently confirm that the unique electronic structure of CoPc and appropriate reaction temperature cooperatively enable a thermodynamic favorable reaction pathway for highly selective methanol production. This work represents an important milestone towards the development of advanced photothermal catalysts for scalable and cost-effective CO2 hydrogenation.

Pd Nanoparticle Size-Dependent H* Coverage for Cu-Catalyzed Nitrate Electro-Reduction to Ammonia in Neutral Electrolyte

Electrochemical conversion of nitrate (NO3 -) to ammonia (NH3) is an effective approach to reduce nitrate pollutants in the environment and also a promising low-temperature, low-pressure method for ammonia synthesis. However, adequate H* intermediates are highly expected for NO3 - hydrogenation, while suppressing competitive hydrogen evolution. Herein, the effect of H* coverage on the NO3RR for ammonia synthesis by Cu electrocatalysts is investigated. The H* coverage can be adjusted by changing Pd nanoparticle sizes. The optimized Pd@Cu with an average Pd size of 2.88 nm shows the best activity for NO3RR, achieving a maximum Faradaic efficiency of 97% (at -0.8 V vs RHE) and an NH3 yield of 21 mg h-1 cm- 2, from an industrial wastewater level of 500 ppm NO3 -. In situ electrochemical experiments indicate that Pd particles with 2.88 nm can promote NO3 - hydrogenation to NH3 via well-modulated coverage of adsorbed H* species. Coupling the anodic glycerol oxidation reaction, ammonium and formate are successfully obtained as value-added products in a membrane electrode assembly electrolyzer. This work provides a feasible strategy for obtaining size-dependent H* intermediates for hydrogenation.