Toward High-Performance and Low-Cost Hydrogen Evolution Reaction Electrocatalysts: Nanostructuring Cobalt Phosphide (CoP) Particles on Carbon Fiber Paper

In this communication, we facily fabricated nanostructured CoP particles (150 to 200 nm) on carbon fiber paper (CFP) for hydrogen evolution reaction (HER) by a simple two-step process via a green route. In the first step, crystalline Co₃O₄ nanocubes (150-200 nm) were loaded on CFP through a hydrothermal process at low temperature (120 °C). Interestingly, crystalline Co₃O₄ nanocubes with a size 150-200 nm exhibited different growth mechanisms in contrast to the crystalline Co₃O₄ nanocubes with a size <100 nm reported earlier. In the second step, these crystalline Co₃O₄ nanocubes were converted to catalytically active CoP particles through chemical vapor deposition (CVD) phosphorization (denoted as CoP/CFP-H). Remarkably, CoP/CFP-H exhibited a low Tafel slope of 49.7 mV/dec and only required overpotentials of 128.1, 144.4, and 190.8 mV to drive geometric current densities of -10, -20, and -100 mA cm^-2, respectively. Besides, the CoP/CFP-H also demonstrated an excellent durability in an acidic environment under 2000 sweeps at a high scan rate (100 mV s^-1) and a 24 h chronopotentiometry testing. For comparison, CoP was also fabricated through the electrodeposition method, followed by CVD phosphorization (denoted as CoP/CFP-E). It was found that the latter had exhibited inferior activity compared to CoP/CFP-H. The good performances of CoP/CFP-H are essentially due to the rational designs of electrode: (i) the applications of highly HER active CoP electrocatalyst, (ii) the intimate contact of nanostructured CoP on carbon fibers, and (iii) the large electrochemical surface area at electrocatalyst/electrolyte interface due to the large retaining of particles features after phosphorization. Notably, the intermediate Co₃O₄/CFP can serve as a platform to develop other cobalt-based functional materials.