Amorphous Nickel-Iron Borophosphate for a Robust and Efficient Oxygen Evolution Reaction

Abstract

Borophosphate materials are promising electrocatalysts for water splitting. Their structural flexibility enable self-adjusting of electronic structure depending on potential. The rich chemistry of borophosphate provides a huge engineering space to tune composition and structure. Herein, amorphized LiNiFe borophosphate (a-LNFBPO) for an efficient and durable oxygen evolution reaction (OER) is first reported. Facile adsorption of oxygen intermediates on the vacancies generated by spontaneous Li dissolution during the OER and regulated electronic structure resulting from the Ni and Fe interaction can boost the OER. The amorphization of LiNiFe borophosphate modifies the electronic structure with metal-oxygen (M-O) bond contraction and the high valence state of the metal cations, which reduces the charge transfer energy between the catalyst and electrolyte. In addition, abundant defects, dangling bonds, and a disordered arrangement induced by amorphization enable an improvement in structural flexibility, facilitating a facile and entire transformation of originally inert species into the active phase during the OER process. The a-LNFBPO@Ni foam shows excellent OER properties requiring only a 215 mV overpotential for generating 10 mA cm(-2) and long-term stability over 300 h.