Templated synthesis of transition metal phosphide electrocatalysts for oxygen and hydrogen evolution reactions

Transition metal phosphides (TMPs) have been regarded as alternative hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalysts owing to their comparable activity to those of noble metal-based catalysts. TMPs have been produced in various morphologies, including hollow and porous nanostructures, which are features deemed desirable for electrocatalytic materials. Templated synthesis routes are often responsible for such morphologies. This paper reviews the latest advances and existing challenges in the synthesis of TMP-based OER and HER catalysts through templated methods. A comprehensive review of the structure–property–performance of TMP-based HER and OER catalysts prepared using different templates is presented. The discussion proceeds according to application, first by HER and further divided among the types of templates used—from hard templates, sacrificial templates, and soft templates to the emerging dynamic hydrogen bubble template. OER catalysts are then reviewed and grouped according to their morphology. Finally, prospective research directions for the synthesis of hollow and porous TMP-based catalysts, such as improvements on both activity and stability of TMPs, design of environmentally benign templates and processes, and analysis of the reaction mechanism through advanced material characterization techniques and theoretical calculations, are suggested.