RESUMO
In this study, an endurance test of 3000 h was conducted on four equivalent proton exchange membrane (PEM) electrolyzers to identify and quantify the impact of an electric ripple current on their durability. Three different typical power converter waveforms and frequencies were explored. Signals were added to the same direct current carrier and also tested for reference. Performance comparison based on polarization curves and electrochemical impedance spectroscopy (EIS) analysis revealed that the ripple current favors degradation. Triangular waveform and a frequency of 10 kHz were identified as the most degrading conditions, leading to a sharp increase in high-frequency resistance (HFR) and the emergence of mass transport limitations due to the enhanced degradation of titanium mesh. Moreover, reversible losses were observed and further explorations are needed to decorrelate them from our observations.
RESUMO
Molecular catalysts have been shown to have high selectivity for CO2 electrochemical reduction to CO, but with current densities significantly below those obtained with solid-state materials. By depositing a simple Fe porphyrin mixed with carbon black onto a carbon paper support, it was possible to obtain a catalytic material that could be used in a flow cell for fast and selective conversion of CO2 to CO. At neutral pH (7.3) a current density as high as 83.7â mA cm-2 was obtained with a CO selectivity close to 98 %. In basic solution (pHâ 14), a current density of 27â mA cm-2 was maintained for 24â h with 99.7 % selectivity for CO at only 50â mV overpotential, leading to a record energy efficiency of 71 %. In addition, a current density for CO production as high as 152â mA cm-2 (>98 % selectivity) was obtained at a low overpotential of 470â mV, outperforming state-of-the-art noble metal based catalysts.