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 in earth, but its application in electrochemical synthesis of ammonia has been still plagued by unsatisfactory Faraday efficiency at ampere-scale current density. Herein we prepared a vertically aligned hematite nanosheet (denoted as Fe2O3-NS) arrays with a high-aspect-ratio (110) crystal facet exposed by one simple in situ electrochemical reconstruction strategy, which delivers unprecedentedly efficient ammonia yield of 189.05 mg h-1 cm-2 companying with Faradaic efficiency of ca. 95% at the 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 the 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 cathode of one Zn-nitrate battery to deliver an outstanding discharge power density of 36.2 mW cm-2.