In Situ Reconstructing NiFe Oxalate Toward Overall Water Splitting

Abstract Surface reconstruction plays an essential role in electrochemical catalysis. The structures, compositions, and functionalities of the real catalytic species and sites generated by reconstruction, however, are yet to be clearly understood, for the metastable or transit state of most reconstructed structures. Herein, a series of NiFe oxalates (Ni x Fe 1‐ x C 2 O 4 , x = 1, 0.9, 0.7, 0.6, 0.5, and 0) are synthesized for overall water splitting electrocatalysis. Whilst Ni x Fe 1‐x C 2 O 4 shows great hydrogen evolution reaction (HER) activity, the in situ reconstructed Ni x Fe 1‐x OOH exhibits outstanding oxygen evolution reaction (OER) activity. As identified by the in situ Raman spectroscopy and quasi‐in situ X‐ray absorption spectroscopy (XAS) techniques, reconstructions from Ni x Fe 1‐x C 2 O 4 into defective Ni x Fe 1‐x OOH and finally amorphous Ni x Fe 1‐x OOH active species (R‐Ni x Fe 1‐x OOH) are confirmed upon cyclic voltammetry processes. Specifically, the fully reconstructed R‐Ni 0.6 Fe 0.4 OOH demonstrates the best OER activity (179 mV to reach 10 mA cm −2 ), originating from its abundant real active sites and optimal d‐band center. Benefiting from the reconstruction, an alkaline electrolyzer composed of a Ni 0.6 Fe 0.4 C 2 O 4 cathode and an in situ reconstructed R‐Ni 0.6 Fe 0.4 OOH anode achieves a superb overall water splitting performance (1.52 V@10 mA cm −2 ). This work provides an in‐depth structure‐property relationship understanding on the reconstruction of catalysts and offers a new pathway to designing novel catalyst.