Efficient overall water splitting over a Mo(IV)-doped Co3O4/NC electrocatalyst

To meet the demand of producing hydrogen at low cost, a molybdenum (Mo)-doped cobalt oxide (Co3O4) supported on nitrogen (N)-doped carbon (x%Mo-Co3O4/NC, where x% represents Mo/Co molar ratio) is developed as an efficient bifunctional electrocatalyst for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). This defect engineering strategy is realized by a facile urea oxidation method in nitrogen atmosphere. Through X-ray diffraction (XRD) refinement and other detailed characterizations, molybdenum ion (Mo4+) is found to be doped into Co3O4 by substituting cobalt ion (Co2+) at tetrahedron site, while N is doped into carbon matrix simultaneously. 4%Mo-Co3O4/NC is the optimized sample to show the lowest overpotentials of 91 and 276 mV to deliver 10 mA cm-2 for HER and OER in 1 M potassium hydroxide solution (KOH), respectively. The overall water splitting cell 4%Mo-Co3O4/NC parallel to 4%Mo-Co3O4/NC displays a voltage of 1.62 V to deliver 10 mA cm(-2) in 1 M KOH. The Mo4+ dopant modulates the electronic structure of active cobalt ion (Co3+) and boosts the water dissociation process during HER, while the increased amount of lattice oxygen and formation of pyridinic nitrogen due to Mo doping benefits the OER activity. Besides, the smaller grain size owing to Mo doping leads to higher electrochemically active surface area (ECSA) on 4%Mo-Co3O4/NC, resulting in its superior bifunctional catalytic activity. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Automated summary

A molybdenum-doped cobalt oxide catalyst supported on nitrogen-doped carbon was developed for efficient hydrogen and oxygen evolution reactions. The optimized sample showed the lowest overpotentials and superior bifunctional catalytic activity. The Mo dopant modulated the electronic structure and increased active surface area, enhancing the water dissociation process and OER activity.