Platinum model-surface and nanoparticle catalysts for the oxygen reduction reaction are enhanced by the presence of concave sites.

The industrialization of the electrochemical reduction of CO 2 toward CO in aqueous electrolytes has recently been started using silver-based gas diffusion electrodes. The performance of a CO 2 -to-CO electrolyzer model on a 10-cm 2 cell size is assessed with respect to operating pressure, achievable current density at faradaic efficiency of CO above 90 %, composition of gas streams and operational lifetime. Operational lifetime has exceeded 1500 h. The first scaling step to 300 cm 2 has been accomplished. The rated power of such a cell is around 300 W.

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.

A copper‐oxide‐based catalyst enriched with paramelaconite (Cu4O3) is presented and investigated as an electrocatalyst for facilitating electroreduction of CO2 to ethylene and other hydrocarbons. Cu4O3 is a member of the copper‐oxide family and possesses an intriguing mixed‐valance nature, incorporating an equal number of Cu+ and Cu2+ ions in its crystal structure. The material is synthesized using a solvothermal synthesis route and its structure is confirmed via powder X‐ray diffraction, transmission electron microscope based selected area electron diffraction, and X‐ray photoelectron spectroscopy. A flow reactor equipped with a gas diffusion electrode is utilized to test a copper‐based catalyst enriched with the Cu4O3 phase under CO2 reduction conditions. The Cu4O3‐rich catalyst (PrC) shows a Faradaic efficiency for ethylene over 40% at 400 mA cm−2. At −0.64 versus reversible hydrogen electrode, the highest C2+/C1 product ratio of 4.8 is achieved, with C2+ Faradaic efficiency over 61%. Additionally, the catalyst exhibits a stable performance for 24 h at a constant current density of 200 mA cm−2.

Currently, platinum group metals play a central role in the electrocatalysis of the oxygen reduction reaction (ORR). Successful design and synthesis of new highly active materials for this process mainly rely on understanding of the so-called electrified electrode/electrolyte interface. It is widely accepted that the catalytic properties of this interface are only dependent on the electrode surface composition and structure. Therefore, there are limited studies about the effects of the electrolyte components on electrocatalytic activity. By now, however, several key points related to the electrolyte composition have become important for many electrocatalytic reactions, including the ORR. It is essential to understand how certain “spectator ions” (e.g., alkali metal cations) influence the electrocatalytic activity and what is the contribution of the electrode surface structure when, for instance, changing the pH of the electrolyte. In this work, the ORR activity of model stepped Pt [ n (111) × (111)] surfaces (where n is equal to either 3 or 4 and denotes the atomic width of the (111) terraces of the Pt electrodes) was explored in various alkali metal (Li + , Na + , K + , Rb + , and Cs + ) hydroxide solutions. The activity of these electrodes was unexpectedly strongly dependent not only on the surface structure but also on the type of the alkali metal cation in the solutions with the same pH, being the highest in potassium hydroxide solutions (i.e., K + ≫ Na + > Cs + > Rb + ≈ Li + ). A possible reason for the observed ORR activity of Pt [ n (111) × (111)] electrodes is discussed as an interplay between structural effects and noncovalent interactions between alkali metal cations and reaction intermediates adsorbed at active catalytic sites.

The electrochemical CO2 reduction reaction (CO2RR) towards CO allows to turn CO2 and renewable energy into feedstock for the chemical industry. Previously shown electrolyzers are capable of continuous operation for more than 1000 h at high faradaic efficiencies and industrially relevant current densities. However, the crossover of educt CO2 into the anode gas has not been investigated in current cell designs: Carbonates (HCO3− and CO32−) are formed at the cathode during CO2RR and are subsequently neutralized at the anode. Thus, CO2 mixes into the anodically evolved O2, which is undesired from commercial perspectives. In this work this chemical transport was suppressed by using a carbonate-free electrolyte. However, a second transport mechanism via physically dissolved gases became apparent. A transport model based on chemical and physical absorption of CO2 and O2 will be proposed and two solutions were experimentally investigated: the use of an anode GDL (A-GDL) and degassing the anolyte with a membrane contactor (MC). Both solutions further reduce the CO2 crossover to the anode below 0.1 CO2 for each cathodically formed CO while still operating at industrially relevant current densities of 200 mA/cm2.

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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.