The development of efficient and low-cost catalysts for water splitting is a fundamental challenge for electrochemical hydrogen production. For commercialization of water electrolyzer, highly efficient catalyst for hydrogen evolution reaction (HER) under basic condition is required. Low-cost molybdenum-based catalysts have attracted much attention, but they have not proven to be sufficiently active or stable in alkaline media. Inspired by biomolecular systems, we now present our successful use of polydopamines, a component of adhesive proteins secreted by marine mussels, to synthesize a new, enhanced molybdenum-based catalyst. Moreover, through combinatorial controlling P and S heteroatom elements, further enhanced electrochemical performance was realized.

Firstly, to study the effect of P incorporation, we synthesized Mo₂C:P using a hydrothermal process. Dopamine (2 mg) was used as a monomer and mixed in tris-(hydroxy-methyl) aminomethane solution (10 mM, pH 8.5). Mo precursors in ammonium heptamolybate (3 mM) and the P precursors in ammonium phosphate (0 to 100 mM) were introduced into the dopamine solution. In order to carbonize the solution, it was dried and then thermally treated in a nitrogen-rich tube furnace at 800 ℃. The electrocatalytic activity of the catalyst was measured using cyclic voltammetry with a rotating disk electrode system in a three-electrode cell at 1M KOH. The 50mM of P sample showed optimal HER catalytic activity, showing the overpotential of 133 mV to attain a current density of 10 mA/cm².

Further improvement could be achieved via S incorporation into the optimized Mo₂C:P catalyst. To find optimal concentration of S element, S precursors in sodium sulfide (0 to 50 mM) were introduced into the dopamine solution with Mo and P precursors and the solution was dried and carbonized at 800 ℃. From the current-potential plot, the overpotential was further decreased (113 mV). From XRD, TEM and XPS analysis, we also identified that the incorporation of S and P changed the crystallinity and electronic structure on the surface, possibly resulting in the improved electrochemical performance.

In conclusion, we have designed a new bio-mimetic Mo₂C:S:P catalyst with enhanced HER properties. The significant catalytic enhancement achieved in this study emphasizes the potential to be explored in strategies applying bioinspired materials as HER catalysts.