Enhancing Electrochemical Hydrogen Evolution Performance of CoMoO<sub>4</sub>-Based Microrod Arrays in Neutral Media through Alkaline Activation
Xin Cui, Yu Cui, Meiling Chen, Rui Xiong, Yucheng Huang, Xiaowang Liu
Abstract
We present that activation of CoMoO4-based microrod arrays in KOH (1.0 M, 2 h) allows us to significantly improve their electrochemical hydrogen evolution performance in phosphate buffer solution (1.0 M, pH = 7.1). The activation mechanism originates from the conversion of the surface layer of CoMoO4 to Co(OH)2 nanosheets, together with the release of Mo3O102– ions into the activation solution. Our experimental and calculated results suggest that the Co(OH)2 nanosheets on the surface of the CoMoO4-based microrod arrays show the ability to improve water molecule disassociation and stabilize the catalytic activity of the two-component catalysts by decreasing their overpotentials in the hydrogen evolution reaction. When extending this strategy to activate P-doped CoMoO4 with a low hydrogen absorption free energy, we report the synthesis of a new class of superior neutral electrochemical hydrogen evolution catalysts of P-doped CoMoO4–Co(OH)2 microrod arrays. We show that a low overpotential of about 30 mV (obtained from bulk electrolysis) is required to deliver a current density of 10 mA cm–2 in the neutral media. By making use of our catalyst and NiFe double hydroxide as cathodic and anodic electrodes, respectively, we fabricated a two-electrode electrolysis device for neutral overall water splitting. Our results showed a low cell voltage of 1.78 V (obtained from bulk electrolysis) that is needed for delivering a current density of about 10 mA cm–2 in the neutral electrolyte, even outperforming the state-of-the-art catalyst combination of Pt/C∥RuO2 in terms of catalytic activity and stability. These findings suggest that our strategy may be utilized as a facile but useful strategy toward the activation of molybdate catalysts to improve their HER performance in both basic and neutral media.