Enhanced Oxygen Evolution Reaction by Efficient Bubble Dynamics of Aligned Nonoxidized Graphene Aerogels

Abstract

Achieving abundant active sites in catalysts by fabricating three-dimensional (3D) microstructures is an efficient approach for improving their oxygen evolution reaction (OER) activities. However, the generated oxygen bubbles in the electrodes are confined in the complex 3D structure, diminishing the catalytic activities and mechanical stability of the electrodes. Therefore, it is essential to rationally design an electrocatalytically active 3D electrode with an optimal microstructure to efficiently remove generated bubbles. Here, we report the fabrication of copper oxide nanoparticles embedded in nonoxidized graphene aerogels (CuONP-NOGAs). The microstructure of CuONP-NOGAs is finely tuned by optimizing the processing parameters of bidirectional freeze casting and its influence on bubble removal behavior efficiency is elucidated. Among electrodes with different degrees of alignment and pore densities, the vertically aligned NOGA with dense porosity exhibits the best efficiency by forming direct open paths for facile bubble movements. The high electrical conductivity combined with a low transfer resistance and uniformly dispersed active particles in CuONP-NOGAs offers excellent OER activities. They deliver a remarkable potential of 1.39 V at 10 mA/cm(2), which is lower than those of the state-of-the-art RuO2 and other copper oxide-based catalysts, as well as ultralong stability of more than 120 h, proving the significance of the effective design of the 3D catalyst microstructure. The present study may provide insights into the design of new 3D microstructures useful for practical application in next-generation energy conversion devices.