Promoting electrocatalytic activity of cobalt cyclotetraphosphate in full water splitting by titanium-oxide-accelerated surface reconstruction

Abstract

The development of efficient electrocatalysts catalyzing the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline media is highly desirable for large-scale hydrogen production from water splitting. Here it is shown that surface reconstruction of cobalt cyclotetraphosphate (Co₂P₄O₁₂) accelerated by titanium oxide (TiO₂) dramatically enhances HER and OER activity in alkaline solution. TiO₂ promotes the formation of metallic cobalt at the TiO₂|Co₂P₄O₁₂ interface in the HER. The resultant composite generates a current density of 20 mA cm⁻² at an overpotential of 81 mV in the alkaline HER, and the overpotential is 157 mV smaller than that of pristine Co₂P₄O₁₂. The activity outperforms that of most non-precious metal electrocatalysts. The synergetic effect between Co, TiO₂, and Co₂P₄O₁₂ reduces the energy barrier of both the Volmer step and Heyrovsky step, inducing performance enhancement. The composite produces a current density of 20 mA cm⁻² at an overpotential of 330 mV in the OER, and the overpotential is 87 mV smaller than that of pristine Co₂P₄O₁₂. The utilization of the composite as a bifunctional electrocatalyst in full water splitting cell is also demonstrated.