Enhanced Synergistic Effect by Facile Tuning of Nickel Doping on Cobalt Phosphide as Electrochemical Catalysts for Hydrogen Evolution Reaction in Alkaline Water Electrolysis

Abstract

The development of efficient and cost-effective electrocatalyst for the hydrogen evolution reaction (HER) is essential for alkaline water electrolysis. Cobalt phosphide (Co2P) is a promising non-noble electrocatalyst material for HER due to its low cost and high stability in alkaline solutions. However, improving the HER performance of Co2P is still challenging due to its catalytic mechanism in which Volmer reaction is the dominated rate-determining step. In this study, we introduced nickel to cobalt phosphide in order to improve its performance as an electrocatalyst because nickel is known to be beneficial for water dissociation (Volmer reaction), while cobalt is beneficial for producing gaseous hydrogen (Heyrovsky or Tafel reaction). This synergistic effect between nickel and cobalt phosphide contributes to enhancing HER performance. Also, it is crucial to find the optimal ratio of nickel and cobalt for maximizing synergistic effect. To facilitate the optimization process, a co-sputtering system was used to fabricate the electrodes. The resulting Ni-doped Co2P showed significantly enhanced HER performance with low overpotential of ~91 mV at 10 mA/cm2 and Tafel slope of ~47 mV/dec compared to pristine Co2P in electrochemical analysis. This enhancement is attributed from the optimized ratio between the sites where water dissociation and adsorbed hydrogen recombination reactions occur. The findings of this study demonstrate that the nickel cobalt phosphide electrode is a promising electrocatalyst for HER in alkaline water electrolysis.