Identifying electrochemical effects in a thermal-electrochemical co-driven system for CO2 capture.

Currently, the most promising amine absorption system for CO2 capture still faces the challenges of heavy steam consumption and a high energy penalty. Thus, a new thermal-electrochemical co-driven system (TECS) for CO2 capture was developed to resolve these problems. In the TECS, unknown electrochemical behaviors are quite essential to assess the CO2 capture performance. Electrochemical experiments were designed using response surface methodology (RSM) to identify electrochemical effects. The results show that the cathode process is slow and difficult, which is the main limitation in improving the performance of the TECS. Forced convection is necessary to improve the diffusion-controlled process and accelerate desorption. Four factors (Cu(ii) molality, CO2 loading, temperature, KNO3 molality) play an auxo-action role in determining anode and cathode reaction rates. A regression model is developed based on the experimental data, and optimum operating conditions are obtained. Regeneration energy consumption reaches about 1.3 GJ per t CO2, a decline of up to 70% compared with the traditional process. In addition, preliminary CO2 desorption experiments suggest that the mass transfer ascribed to the electrochemical process accounts for over 50% of the overall mass transfer coefficient in the CO2 desorption process.

Urea-Functionalized Silver Catalyst toward Efficient and Robust CO2 Electrolysis with Relieved Reliance on Alkali Cations.

We report a new strategy to improve the reactivity and durability of a membrane electrode assembly (MEA)-type electrolyzer for CO2 electrolysis to CO by modifying the silver catalyst layer with urea. Our experimental and theoretical results show that mixing urea with the silver catalyst can promote electrochemical CO2 reduction (CO2R), relieve limitations of alkali cation transport from the anolyte, and mitigate salt precipitation in the gas diffusion electrode in long-term stability tests. In a 10 mM KHCO3 anolyte, the urea-modified Ag catalyst achieved CO selectivity 1.3 times better with energy efficiency 2.8-fold better than an untreated Ag catalyst, and operated stably at 100 mA cm-2 with a faradaic efficiency for CO above 85% for 200 h. Our work provides an alternative approach to fabricating catalyst interfaces in MEAs by modifying the catalyst structure and the local reaction environment for critical electrochemical applications such as CO2 electrolysis and fuel cells.

Understanding the Effects of Anion Interactions with Ag Electrodes on Electrochemical CO2 Reduction in Choline Halide Electrolytes.

Interactions of electrolyte ions at electrocatalyst surfaces influence the selectivity of electrochemical CO2 reduction (CO2 R) to chemical feedstocks like CO. We investigated the effects of anion type in aqueous choline halide solutions (ChCl, ChBr, and ChI) on the selectivity of CO2 R to CO over an Ag foil cathode. Using an H-type cell, we observed that halide-specific adsorption at the Ag surface limits CO faradaic efficiency (FECO ) at potentials more positive than -1.0 V vs. reversible hydrogen electrode (RHE). At these conditions, FECO increased from I- 90 %) in ChCl (at -0.75±0.06 Vvs. RHE) and ChI (at -0.78±0.17 V vs. RHE) could be achieved at a current density of 150 mA cm-2 in a continuous flow-cell electrolyser with Ag nanoparticles on a commercial gas diffusion electrode. This study provides new insights to understand the interactions of anions with catalysts and offers a new method to modify electrocatalyst surfaces.

Catalyst-Electrolyte Interactions in Aqueous Reline Solutions for Highly Selective Electrochemical CO2 Reduction.

Invited for this month's cover is the group of Tom Rufford at the University of Queensland. The image shows how choline chloride and urea in a reline solution interact with the surface of a silver cathode to enhance the selectivity of electrochemical CO2 reduction to CO. The Full Paper itself is available at 10.1002/cssc.201902433.

Catalyst-Electrolyte Interactions in Aqueous Reline Solutions for Highly Selective Electrochemical CO2 Reduction.

Achieving high product selectivities is one challenge that limits viability of electrochemical CO2 reduction (CO2 R) to chemical feedstocks. Here, it was demonstrated how interactions between Ag foil cathodes and reline (choline chloride + urea) led to highly selective CO2 R to CO with a faradaic efficiency of (96±8) % in 50 wt % aqueous reline at -0.884 V vs. the reversible hydrogen electrode (RHE), which is a 1.5-fold improvement over CO2 R in KHCO3 . In reline the Ag foil was roughened by (i) dissolution of oxide layers followed by (ii) electrodeposition of Ag nanoparticles back on cathode. This surface restructuring exposed low-coordinated Ag atoms, and subsequent adsorption of choline ions and urea at the catalyst surface limited proton availability in the double layer and stabilized key intermediates such as *COOH. These approaches could potentially be extended to other electrocatalytic metals and lower-viscosity deep eutectic solvents to achieve higher-current-density CO2 R in continuous-flow cell electrolyzers.