Corrosion Engineering To Synthesize Ultrasmall and Monodisperse Alloy Nanoparticles Stabilized in Ultrathin Cobalt (Oxy)hydroxide for Enhanced Electrocatalysis

Nanoporous high-entropy alloys and metallic glasses: advanced electrocatalytic materials for electrochemical water splitting

Electrochemical water splitting is a promising approach to convert renewable energy into hydrogen energy and is beneficial for alleviating environmental pollution and energy crises, and is considered a clean method to achieve dual-carbon goals. Electrocatalysts can effectively reduce the reaction energy barrier and improve reaction efficiency. However, designing electrocatalysts with high activity and stability still faces significant challenges, which are closely related to the structure and electronic configuration of catalysts. Nanoporous high-entropy alloys (np-HEAs) and metallic glasses (np-MGs), characterized by long-range chemical disorder intertwined with local chemical order combined with three-dimensional, interconnected nanoporous structure, exhibit distinctive electrocatalytic properties and application potential for electrochemical water splitting. To promote the widespread application of np-HEAs and np-MGs, it is of great significance to rationally design and apply them in the field of electrolytic water splitting. In this review, the basic principles of hydrogen evolution reaction and oxygen evolution reaction as well as the fabrication techniques of np-HEAs and np-MGs are introduced. The recent progress in the efficient application of np-HEAs and np-MGs in electrochemical water splitting, and the current challenges and prospects are summarized. This review will provide theoretical guidance for the development of np-HEAs and np-MGs in electrochemical water splitting applications.

Eight-Component Nanoporous High-Entropy Oxides with Low Ru Contents as High-Performance Bifunctional Catalysts in Zn-Air Batteries

One major challenge in heterogeneous catalysis is to reduce the usage of noble metals while maintaining the overall catalytic stability and efficiency in various chemical environments. In this work, a series of high-entropy catalysts are synthesized by a chemical dealloying method and find the increased entropy effect and non-noble metal contents would facilitate the formation of complete oxides with low crystallinity. Importantly, an optimal eight-component high-entropy oxide (HEO, Al-Ni-Co-Ru-Mo-Cr-Fe-Ti) is identified, which exhibits further enhanced catalytic activity for the oxygen evolution reaction (OER) as compared to the previously reported quinary AlNiCoRuMo and the widely-used commercial RuO₂ catalysts, and at the same time similar catalytic activity for the oxygen reduction reaction (ORR) as the commercial Pt/C with a half-wave potential of 0.87 V. Such high-performance bi-functional catalysts, however, only require a half loading amount of Ru as compared to the quinary AlNiCoRuMo, due to the underlying Cr-Fe synergistic effects on tuning the electronic structures at active surface sites, as revealed by the first-principles density functional theory calculations of the authors. The eight-component HEO also demonstrates excellent stability under continuous electrochemical working conditions, suitable for a wide range of applications such as metal-air batteries.

MOF-Derived 2D/3D Hierarchical N-Doped Graphene as Support for Advanced Pt Utilization in Ethanol Fuel Cell

Development of bifunctional catalysts with low platinum (Pt) content for the ethanol oxidation reaction (EOR) and the oxygen reduction reaction (ORR) is highly desirable, yet challenging. Herein, we present structural engineering of a series of two-dimensional/three-dimensional (2D/3D) hierarchical N-doped graphene-supported nanosized Pt₃Co alloys and Co clusters (PtCo@N-GNSs) via a hydrolysis-pyrolysis route. For the ORR, the optimal PtCo@N-GNS exhibits a high mass activity of 3.01 A mg_Pt^-1, which is comparable to the best Pt-based catalyst obtained through sophisticated synthesis. It also possesses excellent stability with minor decay after 50 000 cyclic voltammograms (CV) cycles in acidic medium. For the EOR, PtCo@N-GNS achieves the highest mass-specific and area-specific activities of 1.96 A mg_Pt^-1 and 5.75 mA cm^-2, respectively, among all of the reported EOR catalysts to date. The unique 2D/3D hierarchy, high Pt utilization, and valid encapsulation of nanosized Pt₃Co/Co synergistically contribute to the robust ORR and EOR activities of the present PtCo@N-GNS. A direct ethanol fuel cell based on PtCo@N-GNS delivers a high open-circuit potential of 0.9 V, a stable power density of 10.5 mW cm^-2, and an excellent rate performance, implying the feasibility of the bifunctional PtCo@N-GNS. This work offers a new strategy for designing an ultralow Pt loading yet highly active and durable catalyst for ethanol fuel cell application.

Enhancing Electrochemical Hydrogen Evolution Performance of CoMoO4-Based Microrod Arrays in Neutral Media through Alkaline Activation

We present that activation of CoMoO₄-based microrod arrays in KOH (1.0 M, 2 h) allows us to significantly improve their electrochemical hydrogen evolution performance in phosphate buffer solution (1.0 M, pH = 7.1). The activation mechanism originates from the conversion of the surface layer of CoMoO₄ to Co(OH)₂ nanosheets, together with the release of Mo₃O₁₀^2- ions into the activation solution. Our experimental and calculated results suggest that the Co(OH)₂ nanosheets on the surface of the CoMoO₄-based microrod arrays show the ability to improve water molecule disassociation and stabilize the catalytic activity of the two-component catalysts by decreasing their overpotentials in the hydrogen evolution reaction. When extending this strategy to activate P-doped CoMoO₄ with a low hydrogen absorption free energy, we report the synthesis of a new class of superior neutral electrochemical hydrogen evolution catalysts of P-doped CoMoO₄-Co(OH)₂ microrod arrays. We show that a low overpotential of about 30 mV (obtained from bulk electrolysis) is required to deliver a current density of 10 mA cm^-2 in the neutral media. By making use of our catalyst and NiFe double hydroxide as cathodic and anodic electrodes, respectively, we fabricated a two-electrode electrolysis device for neutral overall water splitting. Our results showed a low cell voltage of 1.78 V (obtained from bulk electrolysis) that is needed for delivering a current density of about 10 mA cm^-2 in the neutral electrolyte, even outperforming the state-of-the-art catalyst combination of Pt/C∥RuO₂ in terms of catalytic activity and stability. These findings suggest that our strategy may be utilized as a facile but useful strategy toward the activation of molybdate catalysts to improve their HER performance in both basic and neutral media.

Cation-Modulated HER and OER Activities of Hierarchical VOOH Hollow Architectures for High-Efficiency and Stable Overall Water Splitting

Atom-scale modulation of electronic regulation in nonprecious-based electrocatalysts is promising for efficient catalytic activities. Here, hierarchically hollow VOOH nanostructures are rationally constructed by partial iron substitution and systematically investigated for electrocatalytic water splitting. Benefiting from the hierarchically stable scaffold configuration, highly electrochemically active surface area, the synergistic effect of the active metal atoms, and optimal adsorption energies, the 3% Fe (mole ratio) substituted electrocatalyst (VOOH-3Fe) exhibits a low overpotential of 90 and 195 mV at 10 mA cm^-2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline media, respectively, superior than the other samples with a different substituted ratio. To the best of current knowledge, 195 mV overpotential at 10 mA cm^-2 is the best value reported for V or Fe (oxy)hydroxide-based OER catalysts. Moreover, the electrolytic cell employing the VOOH-3Fe electrode as both the cathode and anode exhibits a cell voltage of 0.30 V at 10 mA cm^-2 with a remarkable stability over 60 h. This work heralds a new pathway to design efficient bifunctional catalysts toward overall water splitting.

Hierarchical Nanoporous V2O3 Nanosheets Anchored with Alloy Nanoparticles for Efficient Electrocatalysis

Exploring low-cost bifunctional electrocatalysts for efficient water splitting still faces arduous challenges. Herein, a general and straightforward method is developed to prepare 3D hierarchical nanoporous V₂O₃ nanosheets anchored with different alloy nanoparticles by adopting metal-ion-doped zinc-vanadium (oxy)hydroxides as precursors. To demonstrate this concept, we produced nanoporous V₂O₃ nanosheets dotted with NiFe alloy nanoparticles through high-temperature reduction and free corrosion. Due to the increased number of active sites, accelerated mass transfer originating from the designed nanoporous architecture, and the metallic property of the V₂O₃ matrix, the NiFe@V₂O₃ hybrid exhibits excellent electrocatalytic performances for both oxygen and hydrogen evolution reactions. When adopting the NiFe@V₂O₃ as a bifunctional electrode for overall water splitting, it only requires a cell voltage of 1.56 V to reach 10 mA cm^-2. This work provides a general and practical way to prepare high-efficient and low-cost electrocatalysts.