Phosphorus and Yttrium Codoped Co(OH)F Nanoarray as Highly Efficient and Bifunctional Electrocatalysts for Overall Water Splitting

Rational design and synthesis of bifunctional electrocatalysts with high efficiency and low-cost for overall water splitting is still a challenge. A simple approach is reported to prepare a phosphorus and yttrium codoped cobalt hydroxyfluoride (YP-Co(OH)F) nanoarray on nickel foam, which displays high-performance for both hydrogen evolution reaction (HER) and oxygen evolution reaction in alkaline solution. The codoping of yttrium and phosphorus into Co(OH)F leads to a tuned electronic environment and favorable electron transfer, thus resulting in superior water splitting activity. The YP-Co(OH)F electrode only requires an overpotential of 238 mV to reach a current density of 10 mA cm⁻² (η₁₀), much smaller than RuO₂ (302 mV). Moreover, it displays an overpotential of 55 mV at η₁₀ for HER, similar to that of Pt/C. When YP-Co(OH)F is used as both anode and cathode in a two-electrode configuration, it only demands a cell potential of 1.54 V at η₁₀, lower than the IrO₂||Pt/C couple (1.6 V) as well as other recently reported electrocatalysts. It even maintains stable water splitting for 300 h. Such a two-electrode device can be easily driven by a 1.5 V silicon solar cell in sunlight, proving the potential of the promising catalyst for large-scale electrolytic water splitting.