Inverting Destructive Electrochemical Reconstruction of Niobium Nitride Catalyst to Construct Highly Efficient HER/OER Catalyst

Abstract

Electrochemical reconstruction (ECR) is an inevitable phenomenon and also a post-synthetic method in generating real-time active catalysts from pristine materials for various industrial electrochemical processes. Constructive ECRs have commonly been reported in literature, but destructive ECR, especially in the case of non-oxide (S, Se, P, N, etc.) materials, has often gone unnoticed due to insufficient understanding of the process. Herein, we demonstrated an “active site optimization” concept for transforming a destructive ECR into a constructive ECR while using oxygen evolution reaction (OER) as a model electrochemical process. Under alkaline H2 evolution conditions, pristine Nb4N5 does not undergo electrochemical reconstruction and exhibits an outstanding performance that reached a current density of −10 mA cm−2 at 7 mV of overpotential (without iR-correction). However, under alkaline OER conditions, pristine niobium nitride is subjected to destructive ECR and formed inactive KNbO3 species. The incorporation of Fe ion has re-directed the destructive ECR toward a constructive path by developing new active sites. The Fe-incorporated real-time catalyst resulted in an enhanced catalytic OER reaction that reached a current density of 1 A/cm2 with an overpotential of 438 mV. This work provided a comprehensive explanation on the detrimental impact of ECR on electrochemical reactivity of pristine catalysts, and simultaneously presented a conceptual demonstration of a potential strategy to re-direct an ECR path toward a desired direction that improves catalytic activity.