A trace of Pt can significantly boost RuO2 for acidic water splitting

Partial Exsolution Enables Superior Bifunctionality of Ir@SrIrO3 for Acidic Overall Water Splitting

The pursuit of efficient and durable bifunctional electrocatalysts for overall water splitting in acidic media is highly desirable, albeit challenging. SrIrO3 based perovskites are electrochemically active for oxygen evolution reaction (OER), however, their inert activities toward hydrogen evolution reaction (HER) severely restrict the practical implementation in overall water splitting. Herein, an Ir@SrIrO3 heterojunction is newly developed by a partial exsolution approach, ensuring strong metal-support interaction for OER and HER. Notably, the Ir@SrIrO3-175 electrocatalyst, prepared by annealing SrIrO3 in 5% H2 atmosphere at 175 °C, delivers ultralow overpotentials of 229 mV at 10 mA cm-2 for OER and 28 mV at 10 mA cm-2 for HER, surpassing most recently reported bifunctional electrocatalysts. Moreover, the water electrolyzer using the Ir@SrIrO3-175 bifunctional electrocatalyst demonstrates the potential application prospect with high electrochemical performance and excellent durability in acidic environment. Theoretical calculations unveil that constructing Ir@SrIrO3 heterojunction regulates interfacial electronic redistribution, ultimately enabling low energy barriers for both OER and HER.

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.

Ni/NiO@NC as a highly efficient and durable HER electrocatalyst derived from nickel(II) complexes: importance of polydentate amino-acid ligands

Research on Ni/NiO electrocatalysts has advanced significantly, but the main obstacles to their use and commercialization remain their relatively ordinary activity and stability. In this paper, a chelating structure based on the coordination of multidentate ligands and Ni(II) is proposed to limit the growth of Ni and Ni oxide grains. These features reduce the particle size of Ni/NiO, increase particle dispersion, and maintain the high activity and stability of the catalyst. Aspartic acid, as a polydentate ligand, could coordinate with Ni2+ to form structurally stable chelate rings. The latter can limit grain growth, but also coat the active core with thin carbon layers after calcination to further achieve the confinement and protection of nanoparticles. The hydrogen evolution overpotential of prepared nitrogen-doped graphitized carbon shells (Ni/NiO@NC) nanoparticles was 100 mV (vs. RHE) when the current density was 10 mA cm-2 in 1 M KOH. The hydrogen evolution overpotential increased by only 4 mV after 6000 continuous cyclic-voltammetry scans. Moreover, when coated on different conductive substrates, the overpotential of this catalyst dropped to 34.6 mV (vs. RHE) at a current density of 10 mV cm-2. The lowest overpotential of the composite was only 194.9 mV at a current density of 100 mA cm-2, which is comparable with that of noble metal-based electrocatalysts. This work provides a plausible method for designing high-performance electrocatalysts of small size.

Heterostructured CoFeP/CoP as an Electrocatalyst for Hydrogen Evolution in Alkaline Media

Developing highly efficient and persistent transition-metal-phosphide (TMP)-based electrocatalysts is critical for the hydrogen evolution reaction (HER) via water splitting in alkaline media. Herein, we constructed a unique heterostructured CoFeP/CoP grown on a nickle foam (NF) via hydrothermal and dipping methods followed by phosphorization at different temperatures for HER. The experimental results exhibit that the HER activity of CoFeP/CoP-400 is accelerated after the construction of heterostructures. The unique heterostructure provides plentiful active sites and a large surface area, which are beneficial for HER in 1.0 M KOH. CoFeP/CoP-400 displays a small overpotential of 78 mV at a current density of 10 mA cm^-2 and a smaller Tafel slope of 55.5 mV dec^-1. Moreover, CoFeP/CoP-400 shows excellent stability with a long-term operating time of 12 h. This work provides an effective method for the construction of TMPs with heterostructures for promoting energy conversion.

Recent Advances Regarding Precious Metal-Based Electrocatalysts for Acidic Water Splitting

Electrochemical water splitting has wide applicability in preparing high-density green energy. The Proton exchange membrane (PEM) water electrolysis system is a promising technique for the generation of hydrogen due to its high electrolytic efficiency, safety and reliability, compactness, and quick response to renewable energy sources. However, the instability of catalysts for electrochemical water splitting under operating conditions limits their practical applications. Until now, only precious metal-based materials have met the requirements for rigorous long-term stability and high catalytic activity under acid conditions. In this review, the recent progress made in this regard is presented and analyzed to clarify the role of precious metals in the promotion of the electrolytic decomposition of water. Reducing precious metal loading, enhancing catalytic activity, and improving catalytic lifetime are crucial directions for developing a new generation of PEM water electrolysis catalysts. A summary of the synthesis of high-performance catalysts based on precious metals and an analysis of the factors affecting catalytic performance were derived from a recent investigation. Finally, we present the remaining challenges and future perspectives as guidelines for practical use.