Effective perspiration is essential to uphold the stability of zero-gap MEA-based cathodes used in CO2 electrolysers.

The application of gas diffusion electrodes (GDEs) for the electrochemical reduction of CO2 to value-added products creates the possibility of achieving current densities of a few hundred mA cm-2. To achieve stable operation at such high reaction rates remains, however, a challenging task, due to the flooding of the GDE. In order to mitigate flooding in a zero-gap membrane-electrode assembly (MEA) configuration, paths for effective electrolyte perspiration inside the GDE structure have to be kept open during the electrolysis process. Here we demonstrate that apart from the operational parameters of the electrolysis and the structural properties of the supporting gas diffusion layers, also the chemical composition of the applied catalyst inks can play a decisive role in the electrolyte management of GDEs used for CO2 electroreduction. In particular, the presence of excess amounts of polymeric capping agents (used to stabilize the catalyst nanoparticles) can lead to a blockage of micropores, which hinders perspiration and initiates the flooding of the microporous layer. Here we use a novel ICP-MS analysis-based approach to quantitatively monitor the amount of perspired electrolyte that exits a GDE-based CO2 electrolyser, and we show a direct correlation between the break-down of effective perspiration and the appearance of flooding-the latter ultimately leading to a loss of electrolyser stability. We recommend the use of an ultracentrifugation-based approach by which catalyst inks containing no excess amount of polymeric capping agents can be formulated. Using these inks, the stability of electrolyses can be ensured for much longer times

A voltammetric pH sensor for food and biological matrices

Measurement of pH is of fundamental importance in a wide range of environmental, biological and industrial applications. Glass electrode and litmus paper are widely used for this, but the former is difficult to miniaturize, prone to drift and fragile, the latter is inaccurate. This paper describes a pH sensor based on an indoaniline-derivative (4-((4-aminophenyl)imino)-2,6-dimethoxycyclohexa-2,5-dien-1-one), which exploits alternating current voltammetry to measure pH in the range between 2 and 12. The synthetized indoaniline-derivative was not genotoxic (A. cepa assay), and the sensor reliably measured pH in milk, tea, orange juice, blood, urine and saliva. Results were comparable with those obtained with a glass electrode calibrated with certified solutions (maximum relative standard deviation of 3 % and accuracy less than 0.2 pH unit). The sensor had negligible hysteresis, an almost Nernstian sensitivity (56 mV/pH) and was fully functional after a two-month storage. Sensor response showed a limited dependence on temperature (0.14 mV per pH unit and °C) and limited sensitivity to possible interferents such as lithium and sodium ions; its response to these was similar to that of a glass electrode, and was absent for ascorbic acid