Manganese-Doped Bimetallic (Co,Ni)2P Integrated CoP in N,S Co-Doped Carbon: Unveiling a Compatible Hybrid Electrocatalyst for Overall Water Splitting

Rational design of highly efficient noble-metal-unbound electrodes for hydrogen and oxygen production at increased current density is crucial for robust water-splitting. A facile hydrothermal and room-temperature aging method is presented, followed by chemical vapor deposition (CVD), to create a self-sacrificed hybrid heterostructure electrocatalyst. This hybrid material, (Mn-(Co,Ni)2P/CoP/(N,S)-C), comprises manganese-doped cobalt nickel phosphide (Mn-(Co,Ni)2P) nanofeathers and cobalt phosphide (CoP) nanocubes embedded in a nitrogen and sulfur co-doped carbon matrix (N,S)-C on nickel foam. The catalyst exhibits excellent performance in both the hydrogen evolution reaction (HER; η10 = 61 mV) and oxygen evolution reaction (OER; η10 = 213 mV) due to abundant active sites, high porosity, and enhanced hetero-interface interaction between Mn-(Co2P-Ni2P) CoP, and (N,S)-C supported by significant synergistic effects observed among different phases through density functional theory (DFT) calculations. Impressively, (Mn-(Co,Ni)2P/CoP/(N,S)-C (+,-) shows an extra low cell voltage of 1.49 V@10 mA cm-2. Moreover, the catalyst exhibits remarkable stability at 100 and 300 mA cm-2 when operating as a single stack cell electrolyzer. The superior electrochemical activity is attributed to the enhanced electrode-electrolyte interface among the multiple phases of the hybrid structure.

Cobalt-Iron-Phosphate Hydrogen Evolution Reaction Electrocatalyst for Solar-Driven Alkaline Seawater Electrolyzer

Seawater splitting represents an inexpensive and attractive route for producing hydrogen, which does not require a desalination process. Highly active and durable electrocatalysts are required to sustain seawater splitting. Herein we report the phosphidation-based synthesis of a cobalt–iron–phosphate ((Co,Fe)PO₄) electrocatalyst for hydrogen evolution reaction (HER) toward alkaline seawater splitting. (Co,Fe)PO₄ demonstrates high HER activity and durability in alkaline natural seawater (1 M KOH + seawater), delivering a current density of 10 mA/cm² at an overpotential of 137 mV. Furthermore, the measured potential of the electrocatalyst ((Co,Fe)PO₄) at a constant current density of −100 mA/cm² remains very stable without noticeable degradation for 72 h during the continuous operation in alkaline natural seawater, demonstrating its suitability for seawater applications. Furthermore, an alkaline seawater electrolyzer employing the non-precious-metal catalysts demonstrates better performance (1.625 V at 10 mA/cm²) than one employing precious metal ones (1.653 V at 10 mA/cm²). The non-precious-metal-based alkaline seawater electrolyzer exhibits a high solar-to-hydrogen (STH) efficiency (12.8%) in a commercial silicon solar cell.

Titania-Supported Ni2 P/Ni Catalysts for Selective Solar-Driven CO Hydrogenation

Solar-driven Fischer-Tropsch synthesis (FTS) holds great potential for the sustainable production of fuels from syngas and solar energy. However, the selectivity toward multi-carbon products (C₂₊ ) is often hampered by the difficulty in the regulation of transition metals acting as both light absorption units and active sites. Herein, a partial phosphidation strategy to prepare titania supported Ni₂ P/Ni catalysts for photothermal FTS is demonstrated. Under Xenon lamp or concentrated sunlight irradiation, the optimized catalyst shows a C₂₊ selectivity of 70% at a CO conversion of >20%. Conversely, nickel metal in the absence of Ni₂ P delivers negligible C₂₊ products (≈1%) with methane being the major product (>90%). Structural characterization and density functional theory calculation reveal that the partial phosphidation allows exposed metallic Ni to be active for CO adsorption and activation, while the existence of Ni₂ P/Ni interface is responsible to inhibit CO methanation and promote C-C coupling of adsorbed *CH intermediates. This work introduces a novel phosphidation strategy for nickel-based photothermal catalysts in efficiently harnessing solar energy, and regulating the reaction pathways for CO hydrogenation to deliver high value products.

Design and Mechanistic Study of Highly Durable Carbon-Coated Cobalt Diphosphide Core-Shell Nanostructure Electrocatalysts for the Efficient and Stable Oxygen Evolution Reaction

The facile synthesis of hierarchically functional, catalytically active, and electrochemically stable nanostructures holds a tremendous promise for catalyzing the efficient and durable oxygen evolution reaction (OER) and yet remains a formidable challenge. Herein, we report the scalable production of core-shell nanostructures composed of carbon-coated cobalt diphosphide nanosheets, C@CoP₂, via three simple steps: (i) electrochemical deposition of Co species, (ii) gas-phase phosphidation, and (iii) carbonization of CoP₂ for catalytic durability enhancement. Electrochemical characterizations showed that C@CoP₂ delivers an overpotential of 234 mV, retains its initial activity for over 80 h of continuous operation, and exhibits a fast OER rate of 63.8 mV dec^-1 in base.

One-Step Facile Synthesis of Cobalt Phosphides for Hydrogen Evolution Reaction Catalysts in Acidic and Alkaline Medium

Catalysts for hydrogen evolution reaction are in demand to realize the efficient conversion of hydrogen via water electrolysis. In this work, cobalt phosphides were prepared using a one-step, scalable, and direct gas-solid phosphidation of commercially available cobalt salts. It was found that the effectiveness of the phosphidation reaction was closely related to the state of cobalt precursors at the reaction temperature. For instance, a high yield of cobalt phosphides obtained from the phosphidation of cobalt(II) acetate was related to the good stability of cobalt salt at the phosphidation temperature. On the other hand, easily oxidizable salts (e.g., cobalt(II) acetylacetonate) tended to produce a low amount of cobalt phosphides and a large content of metallic cobalt. The as-synthesized cobalt phosphides were in nanostructures with large catalytic surface areas. The catalyst prepared from phosphidation of cobalt(II) acetate exhibited an improved catalytic activity as compared to its counterpart derived from phosphidation of cobalt(II) acetylacetonate, showing an overpotential of 160 and 175 mV in acidic and alkaline electrolytes, respectively. Both catalysts also displayed an enhanced long-term stability, especially in the alkaline electrolyte. This study illustrates the direct phosphidation behavior of cobalt salts, which serve as a good vantage point in realizing the large-scale synthesis of transition-metal phosphides for high-performance electrocatalysts.