Highly Durable and Efficient Ni-FeOx/FeNi3 Electrocatalysts Synthesized by a Facile In Situ Combustion-Based Method for Overall Water Splitting with Large Current Densities

Unlocking Fe(III) Ions Improving Oxygen Evolution Reaction Activity and Dynamic Stability of Anodized Nickel Foam

Fe has been reported to play a crucial role in improving the catalytic activity and stability of Ni/Co-based electrocatalysts for the oxygen evolution reaction (OER), while the Fe effect remains intangible. Here, we design several experiments to identify the activity and stability improvement using porous anodized nickel foam (ANF) as the electrode and 1.0 M KOH containing 1000 μM Fe(III) ions as the electrolyte. Systematic investigations reveal that Ni sites serve as hosts to capture Fe ions to create active FeNi-based intermediates on the surface of ANF to improve the OER activity significantly, and Fe ions regulate catalytic equilibrium and maintain the stability for a long time. The system exhibits 242 and 343 mV overpotentials to reach 10 and 1000 mA cm-2 current densities and a robust stability of 360 h at an industrially suitable current density (1000 mA cm-2). This work expands insights into the Fe(III) catalysis effect on the OER efficiency of Ni-based catalysts and provides an economical and practical way to commercial application.

Construction of hierarchical NCMTs@MoO2/FeNi3 tubular heterostructures for enhanced performance in catalysis and protein adsorption

A new type of hybrid material (NCMTs@MoO2/FeNi3) with a multi-layer heterostructure was designed and fabricated via a one-step pyrolysis process using FeOOH/NiMoO4@PDA as the precursor. FeOOH/NiMoO4@PDA was prepared by the solvothermal method, followed by the nickel-ion etching method coupled with the polymerization of dopamine (DA). The as-obtained material was made of nitrogen-doped carbon nanotubes embedded with FeNi3 and MoO2 nanoparticles (NPs). Notably, the FeNi3 NPs exhibited significantly improved performance in the reduction of 4-nitrophenol (4-NP) and adsorption of histidine-rich protein as well as provided appropriate magnetism resources. The MoO2 NPs imparted a metallic nature with excellent conductivity, and the N-doped mesoporous carbon microtubes also improved conductivity and facilitated mass transfer, thus leading to enhanced performance in catalysis. Benefiting from the 1D hierarchical porous structure and compositional features, the NCMTs@MoO2/FeNi3 composites exhibited excellent performance in 4-NP reduction and protein adsorption via specific metal affinity between the polyhistidine groups of proteins and the FeNi3 NPs. The result presented here indicates that the strategy of combining tailored components, heterostructuring, and carbon integration is a promising way to obtain high-performance composites for other energy-related applications.

FeNi2S4-A Potent Bifunctional Efficient Electrocatalyst for the Overall Electrochemical Water Splitting in Alkaline Electrolyte

For a carbon-neutral society, the production of hydrogen as a clean fuel through water electrolysis is currently of great interest. Since water electrolysis is a laborious energetic reaction, it requires high energy to maintain efficient and sustainable production of hydrogen. Catalytic electrodes can reduce the required energy and minimize production costs. In this context, herein, a bifunctional electrocatalyst made from iron nickel sulfide (FeNi2S4 [FNS]) for the overall electrochemical water splitting is introduced. Compared to Fe2NiO4 (FNO), FNS shows a significantly improved performance toward both OER and HER in alkaline electrolytes. At the same time, the FNS electrode exhibits high activity toward the overall electrochemical water splitting, achieving a current density of 10 mA cm-2 at 1.63 V, which is favourable compared to previously published nonprecious electrocatalysts for overall water splitting. The long-term chronopotentiometry test reveals an activation followed by a subsequent stable overall cell potential at around 2.12 V for 20 h at 100 mA cm-2.

Crystalline metal phosphide-coated amorphous iron oxide-hydroxide (FeOOH) with oxygen vacancies as highly active and stable oxygen evolution catalyst in alkaline seawater at high current density

In this study, we employed a straightforward phosphorylation approach to achieve a dual objective: constructing c-a heterostructures consisting of crystalline Ni12P5 and amorphous FeOOH, while simultaneously enhancing oxygen vacancies. The resulting oxygen evolution reaction (OER) catalyst, Ni12P5/FeOOH/NF, exhibited remarkable performance with current densities of 500 mA cm-2 in both 1 M KOH and 1 M KOH + seawater, requiring low overpotentials of only 288 and 365 mV, respectively. Furthermore, Ni12P5/FeOOH/NF exhibited only a slight increase in overpotential, with increments of 18 mV and 70 mV in 1 M KOH after 15 and 150 h, and 32 mV and 108 mV in 1 M KOH + seawater at 500 mA cm-2 after 15 and 150 h, respectively. This minimal change can be attributed to the stabilized c-a structure, the protective coating of Ni12P5, and superhydrophilic. Through in-situ Raman and ex-situ XPS analysis, we discovered that Ni12P5/FeOOH/NF can undergo a reconfiguration into an oxygen vacancy-rich (Fe/Ni)OOH phase during OER process. The elevated OER activity is mainly due to the contribution of the oxygen vacancy-rich (Fe/Ni)OOH phase from the reconfigure of the Ni12P5/FeOOH/NF. This finding emphasizes the critical role of oxygen vacancies in facilitating the production of OO species and overcoming the limitations associated with OOH formation, ultimately enhancing the kinetics of the OER.

Material Engineering Strategies for Efficient Hydrogen Evolution Reaction Catalysts

Water electrolysis, a key enabler of hydrogen energy production, presents significant potential as a strategy for achieving net-zero emissions. However, the widespread deployment of water electrolysis is currently limited by the high-cost and scarce noble metal electrocatalysts in hydrogen evolution reaction (HER). Given this challenge, design and synthesis of cost-effective and high-performance alternative catalysts have become a research focus, which necessitates insightful understandings of HER fundamentals and material engineering strategies. Distinct from typical reviews that concentrate only on the summary of recent catalyst materials, this review article shifts focus to material engineering strategies for developing efficient HER catalysts. In-depth analysis of key material design approaches for HER catalysts, such as doping, vacancy defect creation, phase engineering, and metal-support engineering, are illustrated along with typical research cases. A special emphasis is placed on designing noble metal-free catalysts with a brief discussion on recent advancements in electrocatalytic water-splitting technology. The article also delves into important descriptors, reliable evaluation parameters and characterization techniques, aiming to link the fundamental mechanisms of HER with its catalytic performance. In conclusion, it explores future trends in HER catalysts by integrating theoretical, experimental and industrial perspectives, while acknowledging the challenges that remain.

Theoretically Designed Cu10Sn3-Cu-SnOx as Three-Component Electrocatalyst for Efficient and Tunable CO2 Reduction to Syngas

Electrocatalytic transformation of CO2 to various syngas compositions is an exceedingly attractive approach to carbon-neutral recycling. Meanwhile, the achievement of selectivity, stability, and tunability of product ratios using single-component electrocatalysts is challenging. Herein, the theoretically-assisted design of the triple-component nanocomposite electrocatalyst Cu10Sn3-Cu-SnOx that addresses this challenge is presented. It is shown that Cu10Sn3 is a valuable electrocatalyst for suitable CO2 reduction to CO, SnO2 for CO2 reduction to formate at large overpotentials, and that the Cu-SnO2 interface facilitates H2 evolution. Accordingly, the interaction between the three functional components affords tunable CO/H2 ratios, from 1:2 to 2:1, of the produced syngas by controlling the applied potentials and relative contents of functional components. The syngas generation is selective (Faradaic efficiency, FE = 100%) at relatively lower cathodic potentials, whereas formate is the only liquid product detected at relatively higher cathodic potentials. The theoretically guided design approach therefore provides a new opportunity to boost the selectivity and stability of CO2 reduction to tunable syngas.

Synergistic Activation of Inert Iron Oxide Basal Planes through Heterostructure Formation and Doping for Efficient Hydrogen Evolution

Iron oxides have emerged as a very promising and cost-effective alternative to precious metal catalysts for hydrogen production. However, the inert basal plane of iron oxides needs to be activated to enhance their catalytic efficiency. In this study, we employed heterostructure engineering and doped nickel to cooperatively activate the basal planes of iron oxide (Ni-Fe2 O3 /CeO2 HSs) to achieve high hydrogen evolution reaction (HER) activity. The Ni-Fe2 O3 /CeO2 HSs electrocatalyst demonstrates excellent basic HER activity and stability, such as an extremely low overpotential of 43 mV at 10 mA cm-2 current density and corresponding Tafel slope of 58.6 mV dec-1 . The increase in electrocatalyst activity and acceleration of hydrogen precipitation kinetics arises from the dual modulation of Ni doping and heterostructure, which not only modulates the electrocatalyst's electronic structure, but also increases the number and exposure of active sites. Remarkably, the generation of heterogeneous structure makes the catalyst se. The Ni-doped catalyst has not only increased HER activity but also low-temperature resistance. These results suggest that the synergistic activation of inert iron oxide basal planes through heterostructure formation and doping is a feasible strategy. Furthermore, for efficient electrocatalytic water splitting, this technique can be extended to other non-noble metal oxides.

Binary Ni-Co-Based Layered Double Hydroxide Nanoneedle Arrays for High Performance of Oxygen Evolution Reaction

Low-cost and high-performance electrocatalysts are crucial for water-splitting reactions. Some non-precious metal electrocatalysts are proved to be good replacements for noble metal due to the unique electronic structure features and excellent performance. In this work, binary Ni-Co-based layered double hydroxide nanoneedle arrays electrocatalysts are synthesized on Ni foam (NF) via a hydrothermal process. The microstructure and the catalytic performance of the catalyst changes significantly by regulating the molar ratio of Ni/Co. The theoretical analysis confirmed that the as-prepared NiCo-LDH nanoneedle arrays reveal a potential behavior in oxygen evolution reaction (OER) at a lower overpotential of 305 mV at 10.0 mA cm^-2 and a Tafel slope of 110.38 mV dec^-1. The double-layer capacitance (C_dl) is 776 mF cm^-2, which indicates that there are many active sites that are exposed on the surface for the electrocatalytic reaction. The results provide an obvious reference value to other types of LDH catalysts for the development of water electrolysis.

Duplex Interpenetrating-Phase FeNiZn and FeNi3 Heterostructure with Low-Gibbs Free Energy Interface Coupling for Highly Efficient Overall Water Splitting

The sluggish kinetics of both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) generate the large overpotential in water electrolysis and thus high-cost hydrogen production. Here, multidimensional nanoporous interpenetrating-phase FeNiZn alloy and FeNi3 intermetallic heterostructure is in situ constructed on NiFe foam (FeNiZn/FeNi3@NiFe) by dealloying protocol. Coupling with the eminent synergism among specific constituents and the highly efficient mass transport from integrated porous backbone, FeNiZn/FeNi3@NiFe depicts exceptional bifunctional activities for water splitting with extremely low overpotentials toward OER and HER (η1000 = 367/245 mV) as well as the robust durability during the 400 h testing in alkaline solution. The as-built water electrolyzer with FeNiZn/FeNi3@NiFe as both anode and cathode exhibits record-high performances for sustainable hydrogen output in terms of much lower cell voltage of 1.759 and 1.919 V to deliver the current density of 500 and 1000 mA cm-2 as well long working lives. Density functional theory calculations disclose that the interface interaction between FeNiZn alloy and FeNi3 intermetallic generates the modulated electron structure state and optimized intermediate chemisorption, thus diminishing the energy barriers for hydrogen production in water splitting. With the merits of fine performances, scalable fabrication, and low cost, FeNiZn/FeNi3@NiFe holds prospective application potential as the bifunctional electrocatalyst for water splitting.

Janus (Mo/β-Mo2C)@C heterostructure as an efficient electrocatalyst for the hydrogen evolution reaction in acidic and alkaline media

To explore low-cost, high-efficiency, and noble-metal-free catalysts for electrocatalytic water splitting in both acidic and alkaline media, the metal-metal carbide Janus hierarchical structure comprising Mo andβ-Mo₂C embedded on a carbon layer (Mo/β-Mo₂C)@C is synthesized by a hydrothermal reaction and subsequent low-temperature magnesium thermic process. Systematic characterization by XRD, XPS, Raman scattering, and SEM/TEM reveals the successful formation of metallic Mo andβ-Mo₂C nanoparticles. The synthesized (Mo/β-Mo₂C)@C has a large specific surface area and boasts highly efficient hydrogen evolution reaction activity including low overpotentials of 152 and 171 mV at a current density of 10 mA cm^-2and small Tafel slopes of 51.7 and 63.5 mV dec^-1in acidic and alkaline media, respectively. In addition, the catalyst shows outstanding stability for 48 h in both acidic and alkaline media. The excellent catalytic activity originates from more active sites and greater electron conductivity bestowed by the carbon layer, which also improves the long-term stability in both acidic and alkaline solutions.

Effective Electro-Activation Process of Hydrogen Peroxide/Peroxydisulfate Induced by Atomic Hydrogen for Rapid Oxidation of Norfloxacin over the Carbon-Based Pd Nanocatalyst

Peroxydisulfate (PDS) can be activated by electrochemistry, for which using atom H* as an activator is feasibly favorable in theoretical and experimental applications. Studies have shown that atomic H* can cleave the peroxide bond as a single-electron reducing agent in Na₂S₂O₈ to generate SO₄^•-, thus achieving the degradation of pollutants. Herein, Pd nanoparticles synthesized by in an in situ solution were dispersed in carbon black and then loaded on carbon felt, called Pd/C@CF, as the cathode for peroxydisulfate activation. This showed an ideal degradation effect on a small electrode (10 mm × 10 mm). Cyclic voltammetry (CV) and linear sweep voltammetry (LSV) tests were taken to verify the significant increase in the yield of the reduction of Na₂S₂O₈ by H*. The degradation experiments and free-radical scavenging experiment confirmed that the atomic H* was the dominant component triggering the activation of PDS to generate SO₄^•-. A Pd/C@CF composite electrodes have low pH dependence, high stability and recyclability, etc., which has many potential practical applications in wastewater treatment. In addition, H* can also reduce H₂O₂ to •OH by breaking the peroxide bond, so the removal of pollutants by the same amount of H₂O₂ and Na₂S₂O₈ under the same conditions is compared, and their application prospects are analyzed and compared.