Vertically aligned hematite nanosheets with (110) facets controllably exposed for ammonia synthesis with high Faraday efficiency beyond 2.5 A cm−2

Abstract

Hematite has been widely investigated for promising (photo)electrocatalysis due to its good robustness and abundant element content on earth, but its application in the electrochemical synthesis of ammonia is still plagued by unsatisfactory Faraday efficiency at ampere-scale current density. Herein, we prepared vertically aligned hematite nanosheet (denoted as Fe₂O₃-NS) arrays with a high-aspect-ratio (110) crystal facet exposed by applying a simple in situ electrochemical reconstruction strategy, which delivers unprecedentedly efficient ammonia yield of 189.05 mg h⁻¹ cm⁻² accompanied by faradaic efficiency of ca. 95% at a current density of exceeding 2.5 A cm⁻², outperforming the state-of-the-art Fe-based electrocatalysts. It is experimentally and theoretically revealed that the exposed (110) crystal plane of Fe₂O₃-NS is favorable for the adsorption and activation of intermediate species during electrocatalysis, and its vertically aligned nanosheet arrays provide abundant active sites and favorable charge transfer channels. The as-obtained hematite nanosheet arrays were finally employed as the cathode of a Zn–nitrate battery to deliver an outstanding discharge power density of 36.2 mW cm⁻².