Electrochemically tuned cobalt hydroxide carbonate with abundant grain boundaries for highly efficient electro-oxidation of hydrazine

Grain boundaries bear many active sites for surface reactions (e.g. electrocatalysis and energy storage), and increasing the grain boundaries has become an important strategy to tune the number of surface active sites and the reaction kinetics. Herein, we show that a simple in situ electrochemical tuning method can be used to turn Co(OH)x(CO3)0.5(2−x) crystals into interconnected ultrafine nanoparticles with enriched grain boundaries. The grain boundaries offer numerous unparalleled active sites for highly efficient electro-oxidation of hydrazine. The electrochemically-tuned Co(OH)x(CO3)0.5(2−x) shows an onset potential (−1.12 V vs. Ag/AgCl) 180 mV smaller than that of the pristine Co(OH)x(CO3)0.5(2−x), and delivers a high current density of 62.4 mA cm−2 at −0.90 V vs. Ag/AgCl, which is 27 times higher than that of the pristine Co(OH)x(CO3)0.5(2−x). This work produces the most active non-metallic catalyst for hydrazine oxidation with catalytic activity comparable to the state-of-the-art catalysts. Moreover, our electrochemical tuning method is applicable to other materials (e.g. Co3O4, Co(OH)2 and Ni(OH)2).