Morphology adjustable CoxN with 3D mesoporous structure and amorphous N-doped carbon for overall water splitting

[Display omitted] •Hierarchical structure of CoxN was successfully synthesized at various temperatures.•The 3D mesoporous structure gives CoxN a large specific surface area.•Amorphous N-doped carbon improves charge transfer ability and stability of CoxN.•The morphology-controlled Co3N exhibited superior electrocatalytic performance. In order to improve the efficiency of the water splitting system, many researchers have focused on controlling the nanostructure of the catalysts, which could reduce the overpotential value of the overall water splitting process. Herein, we report the characteristics of the overall water splitting of cobalt nitrides synthesized in the same way but differing only in the temperature of nitridation. Hierarchical phases (Co3N, Co3N/Co4N, and Co4N) and structures (mesoporous nanocubes, porous nanocubes, and aggregated particles) of CoxN with different thickness of amorphous N-doped carbon allowed CoxN to have different overpotential values (419 mV, 557 mV, and 606 mV at a current density of 10 mA∙cm−2), which is in contrast to known theoretical electrical properties. Our research about the comparison of hierarchical structure of CoxN offers the potential as advanced electrocatalysts for many materials that have not yet been morphologically controlled.