Replacing oxygen evolution with sodium sulfide electro-oxidation toward energy-efficient electrochemical hydrogen production: Using cobalt phosphide nanoarray as a bifunctional catalyst

Water splitting is an important process to produce hydrogen fuels and oxygen evolution reaction (OER), the anodic half reaction, is identified as the bottleneck for its kinetic and energetic complexity in improving the overall efficiency. In this communication, we report that cobalt phosphide nanoarray in situ grown on Ti mesh (CoP NA/TM) behaves as a durable robust non-noble-metal electrocatalyst for sodium sulfide (Na2S) oxidation with the need of potential of 1.31 V to drive 20 mA cm−2 in 1.0 M KOH with 50 mM Na2S. The high hydrogen-evolving activity for CoP NA/TM enables it as a bifunctional catalyst electrode for energy-efficient electrochemical hydrogen generation by replacing OER with Na2S oxidation reaction. The CoP NA/TM||CoP NA/TM couple needs a cell voltage of 1.49 V to drive 15 mA cm−2, 210 mV less than of pure water splitting, with strong long-term electrochemical durability and 100% Faradic efficiency for hydrogen evolution.