Growth kinetics of electrochemically generated hydrogen bubbles at increased pressures

Abstract

Bubble growth kinetics has been attracting vast attention in water electrolysis and other gas evolution reactions, but mostly investigated under ambient pressure. For practical scenarios, bubble evolution is usually carried out under high pressure. To better understand the bubble growth kinetics, we monitored the hydrogen bubble evolution process at increased pressures during electrochemical hydrogen production. Unlike the common sense that high pressures could result in smaller bubble size, our results revealed that the increased pressure would increase the aerophilicity of electrode surface, with decreased bubble contact angle from 111° to 89° for 0.1‒2.0 MPa, increased detachment size from 233 to 1207 µm, and reduced growth coefficient from 230 to 10.9 for the high pressures from 0.1 to 3.0 MPa. The steady high-pressure bubble growth kinetics are basically governed by the as-formed supersaturation in bulk solution, which is the balance between the driving force (current density) and the enlarged solubility of bulk solution under high pressure. Insufficient driving force would induce the depletion of bulk supersaturation and stagnate the bubble growth. Further investigation on high-pressure bubble evolution behaviors should shed light on practical industrial electrode design with extended usage life.