Electrochemical noise study of the effect of electrode surface wetting on the evolution of electrolytic hydrogen bubbles

Ni and Ni-polytetrafluoroethylene (Ni-PTFE) composite electrodes were used as model systems for the study of the effect of electrode surface wetting on the evolution of electrolytic bubbles. This study was carried out by recording electrochemical noise and video images of the electrode surface. Ni-PTFE electrodes were prepared by a sediment co-deposition method, i.e., by electrodepositing Ni while PTFE particles, initially suspended in the Ni2+ electrolyte, formed a sediment on the electrode and became incorporated in the deposit. SEM images showed that co-deposition of PTFE induced an increase in the deposit roughness. PTFE particles were rather uniformly dispersed in the Ni layer. Their concentration (mass ratio) in the deposits, estimated by EDX, varied almost linearly between 1.7% and 7.1% when the PTFE concentration in the suspension was changed between 1.6% and 8.2%. The analysis of the power spectral density of the fluctuations of the electrolyte resistance, induced by hydrogen-bubble evolution in a I M NaOH solution at a constant current density, showed that the average radius of the H, bubbles detaching from the Ni-PTFE cathodes increased with the PTFE concentration and therefore with the hydrophobicity of the electrodes. As a limiting behaviour observed with PTFE-rich electrodes (with a PTFE concentration as large as 38.5%) the bubble size became comparable with that of the electrode. The video images confirmed that the average size of the detaching gas bubbles determined from the electrochemical noise measurements was correct and showed that coalescence phenomena were quite common and significantly contributed to the overall noise. (c) 2006 Elsevier B.V. All rights reserved.