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Understanding bubbles evolution kinetics on electrodes with varied geometries is of fundamental importance for advanced electrodes design in gas evolution reaction. In this work, the evolution kinetics of electro-generated hydrogen bubbles are recorded in situ on three (i.e. smooth, nanoporous, and nanoarray) Pt electrodes to identify the geometry dependence. The bubble radius shows a time-dependent growth kinetic, which is tightly-connected to the electrode geometry. Among the three electrodes, the smooth one shows a typical time coefficient of 0.5, in consistence with reported values; the nanoporous one shows a time coefficient of 0.47, less than the classic one (0.5); while the nanoarray one exhibits fastest bubble growth kinetics with a time coefficient higher than 0.5 (0.54). Moreover, the nanoarray electrode has the smallest bubble detachment size and the largest growth coefficient (23.3) of all three electrodes. Based on the experimental results, a growth model combined direct bottom- injection with micro-convection is proposed to illustrate the surface geometry dependent coefficients, i.e., the relationship between geometry and bubble evolution kinetics. The direct injection of generated gas molecules from the bottom of bubbles at the three phase boundaries are believed the key to tailor the bubble wetting states and thus determine the bubble evolution kinetics.
We thank Prof. Weng-Feng Lin from Loughborough University and Hongjie Dai from Stanford University for the valuable discussion. This work was supported by the National Natural Science Foundation of China (NSFC), the National Key Research and Development Project (Nos. 2018YFB1502401 and 2018YFA0702002), the Royal Society and the Newton Fund through the Newton Advanced Fellowship award (NAF\ R1\191294), the Program for Changjiang Scholars and Innovation Research Team in the University (No. IRT1205), the Fundamental Research Funds for the Central Universities, and the long-term subsidy mechanism from the Ministry of Finance and the Ministry of Education of China.