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

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 vertical bar 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.