Mesoporous Nanosheet Networked Hybrids of Cobalt Oxide and Cobalt Phosphate for Efficient Electrochemical and Photoelectrochemical Oxygen Evolution

A novel mesoporous nanosheet networked hybrid comprising Co₃ O₄ and Co₃ (PO₄ )₂ is successfully synthesized using a facile and scalable method through calcinating the carbon, cobalt hydroxy carbonate, and cobalt phosphate composite precursor. Electron transfer from Co₃ O₄ to Co₃ (PO₄ )₂ , together with the special networked structure and the porous nature of the nanosheets enable the Co₃ (PO₄ )₂ -Co₃ O₄ hybrid to have a high oxygen evolution reaction (OER) activity and outstanding stability in alkaline electrolyte, e.g., an overpotential of 270 mV at current density of 10 mA cm^-2 , and a Tafel slope of 39 mV dec^-1 , which are superior to most non-noble metal-based OER electrocatalysts reported thus far and as well the commercial RuO₂ electrocatalyst. Furthermore, Co₃ (PO₄ )₂ -Co₃ O₄ hybrid is demonstrated to be used as an efficient cocatalyst to enhance the photoelectrochemical OER performance of BiVO₄ photoanode. A significantly increased photocurrent density of 3.0 mA cm^-2 at 1.23 V (vs reversible hydrogen electrode, RHE), and a potential reduction of 530 mV with respect to that of bare BiVO₄ at the photocurrent density of 0.5 mA cm^-2 are achieved. The electron transfer-induced enhancement of OER by a hybrid structure may pave the new routes for the design and synthesis of low-cost catalysts for electrochemical and photoelectrochemical oxygen evolution.