Local Activities of Hydroxide and Water Determine the Operation of Silver‐Based Oxygen Depolarized Cathodes

Abstract

Local ion activity changes in close proximity to the surface of an oxygen depolarized cathode (ODC) were measured by scanning electrochemical microscopy (SECM). While the operating ODC produces OH ions and consumes O and H O through the electrocatalytic oxygen reduction reaction (ORR), local changes in the activity of OH ions and H O are detected by means of a positioned Pt microelectrode serving as an SECM tip. Sensing at the Pt tip is based on the pH-dependent reduction of PtO and obviates the need for prior electrode modification steps. It can be used to evaluate the coordination numbers of OH ions and H O, and the method was exploited as a novel approach of catalyst activity assessment. We show that the electrochemical reaction on highly active catalysts can have a drastic influence on the reaction environment.

Processes and Their Limitations in Oxygen Depolarized Cathodes: A Dynamic Model‐Based Analysis

“…[9,12] Here, two major effects are identified, leading to the transport limitation of oxygen. chemically active, which supports findings previously reported.…”

“…[9] Because ah omogeneous distribution of the gas-liquid interface and concentrations in the x and y directions is assumed, the specific surfacea rea of the interface (S interface )i sd efined by Equation (2) and represents the phase interface area per geometric cross-sectional area of the electrode: Additionally,o xygen is dissolved in the thin film and transported into the flooded agglomerates, where the ORR occurs.…”

“…(9), (14), and (17)],adynamic implementation of Raoult's law can be obtained. (9), (14), and (17)],adynamic implementation of Raoult's law can be obtained.…”

“…[7] However,r egardless of the great importance of the ORR, the keyd rivers for the observed high current densities of the ODCsa nd the underlying limiting processes are not wellu nderstood.E ssential properties such as the local distribution of the gaseous and liquid phase within the electrode are unknown. [9] The behavior of the ORR and the ODCs in alkaline media have been investigated in several studies:B lizanac et al examined the reactionp athway of the ORR on silver single-crystal surfaces with rotatingr ing disk electrodes. [9] The behavior of the ORR and the ODCs in alkaline media have been investigated in several studies:B lizanac et al examined the reactionp athway of the ORR on silver single-crystal surfaces with rotatingr ing disk electrodes.…”

“…[8] Clausmeyer et al performed examinationsw ith different NaOH concentrations in the electrolyte. [9] However,t he interplay of mass transport, processes at the gas-liquid interface, and reaction kinetics are not well under-Oxygend epolarized cathodes (ODCs) are key components of alkaline fuel cells and metal-air batteries or of chlor-alkaline electrolysis, but suffer from limited oxygen availability at the reactionz one. [9] However,t he interplay of mass transport, processes at the gas-liquid interface, and reaction kinetics are not well under-Oxygend epolarized cathodes (ODCs) are key components of alkaline fuel cells and metal-air batteries or of chlor-alkaline electrolysis, but suffer from limited oxygen availability at the reactionz one.…”