Employing Ag2Cu2O3, a mixed metal oxide, as a template catalyst material for electrochemical reduction of CO enables generation of multi-carbon products with a faradaic efficiency of close to 92%, at a current density of 600 mA cm−2.

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In CO 2 electroreduction it is common to use cation exchange membranes in combination with high-molar electrolytes. In a model polymer electrolyte membrane (PEM) water electrolysis setup, which mimics CO 2 electrolysis in a mixed (mode mix ) and in a separate electrolyte mode (mode sep ), this study investigates how K + -sulfonate interactions increase membrane resistance dependent on the electrolyte concentration. K + -based electrolytes (KHCO 3 , K 2 SO 4 ) are used instead of ultrapure water in the PEM-model electrolyzer. At 1.0 M KHCO 3 , the membrane resistance is increased by 1.7 Ω cm 2 (cathode side only) to 4.2 Ω cm 2 (mode mix ), causing a significant voltage increase that needs to be invested for K + transport over a PFSA membrane. We quantify the underlying ionic interactions to 527-545 mV and observed a further effect, namely a space-charge limitation expressed by a strongly increased voltage, occurring in the case of K + overload when lacking hopping centers for cation transport. Beginning at ca. 300 mA/cm 2 , the current density gets high enough to drive K + back to the cathode side and low enough to prevent large resistive contributions and K + overload. Along with thermodynamic considerations and pHinduced intrinsic operational contributions, the membrane resistance was found to have a significant impact contributing to the total cell voltage V total and proved that current research towards green and scalable CO 2 electrolysis is on a promising way towards broad application.[a] K.

We investigated the cobalt polyoxometalate catalyst Ba8[Co9(H2O)6(OH)3(HPO4)2(PW9O34)3] in oxygen evolution reaction for large‐scale water electrolysis. The catalyst was characterized, yielding BET surfaces (8.37 m2/g), crystal water content (8.38%, 44 H2O), elemental analyses and single crystal structures (space group P1̅, a = 19.901(4) Å, b = 21.177(4) Å, c = 24.036(5) Å, α = 92.689(7)°, β = 108.73(7)°, γ = 117.137(6)°, Co9Na16O196.05P5W27, V = 8310(3) Å2 with z = 2; R2final = 0.001). The catalyst was integrated in an industrially applicable membrane electrode assembly and electrochemically characterized. Polarization studies revealed catalyst dissolution in situ, visible as a current density peak (32.2 mA/cm2, 2.2 V) with subsequent collapse (<5 mA/cm2). Galvanostatic experiments showed voltage increase from 2.5 to > 10 V at 10 mA/cm2 tracing back to acid‐mediated decomposition of the anionic POM oxide framework. We deduced insufficient thermodynamic as well as kinetic stability for industrial requirements in PEM water electrolysis.

The Cover Feature illustrates a study where a PEM water electrolysis model setup was used to quantify the increase in membrane resistance and cell voltage when K+‐based electrolytes are used in combination with a PFSA membrane. Potassium cations are soaked into a PFSA membrane against the electroduffusion direction and occupy sulfonate groups thus blocking proton transport channels. The study provides important insights about energy contributions in CO2 electrolysis applications. More information can be found in the Article by K.‐M. Vetter et al.