Direct synthesis of bismuth nanosheets on a gas diffusion layer as a high-performance cathode for a coupled electrochemical system capable of electroreduction of CO2 to formate with simultaneous degradation of organic pollutants

Coupling Value-Added Anodic Reactions with Electrocatalytic CO2 Reduction

Electrocatalytic CO₂ reduction features a promising approach to realize carbon neutrality. However, its competitiveness is limited by the sluggish oxygen evolution reaction (OER) at anode, which consumes a large portion of energy. Coupling value-added anodic reactions with CO₂ electroreduction has been emerging as a promising strategy in recent years to enhance the full-cell energy efficiency and produce valuable chemicals at both cathode and anode of the electrolyzer. This review briefly summarizes recent progresses on the electrocatalytic CO₂ reduction, and the economic feasibility of different CO₂ electrolysis systems is discussed. Then a comprehensive summary of recent advances in the coupled electrolysis of CO₂ and potential value-added anodic reactions is provided, with special focus on the specific cell designs. Finally, current challenges and future opportunities for the coupled electrolysis systems are proposed, which are targeted to facilitate progress in this field and push the CO₂ electrolyzers to a more practical level.

A highly active copper-nanoparticle-based nitrate reduction electrocatalyst prepared by in situ electrodeposition and annealing

In recent years, copper-based electrodes have attracted intense attention for the electrochemical reduction of nitrate (NO₃^-), the so-called ECRN. However, these electrodes suffer from low activity and selectivity. Herein, we report a novel Cu-based electrode (IE-Cu-400) for the ECRN fabricated by loading Cu-based nanoparticles onto graphite felt using in situ electrodeposition followed by annealing. Compared with traditional Cu-based electrodes, the IE-Cu-400 is comprised of smaller particles and the copper is present in a high oxidation state (Cu²⁺ in CuO). During operation, the CuO is converted to Cu, which is the active ECRN species. In addition, an increased surface area and high density of grain boundaries resulting from the reduction of CuO were observed for IE-Cu-400. This resulted in a 3.38-fold increase in the NO₃^- removal rate and a 1.36-fold increase in NH₄⁺ selectivity. Further analyses revealed that the enhanced ECRN performance of IE-Cu-400 is linked to its increased number of active sites, as well as its improved adsorption and reduction ability for NO₂^-. Moreover, IE-Cu-400 displays high stability for the ECRN. Finally, the produced NH₄⁺ was effectively oxidised to N₂ with approximately 100% selectivity via chlorination. Hence, the two-stage treatment strategy (i.e. ECRN by IE-Cu-400 + chlorination treatment) presented here shows great potential for the complete electrocatalytic denitrification of water. Further, this work highlights the beneficial effect of decreasing the particle size and controlling the surface oxidation of Cu-based catalysts simultaneously for enhancing the ECRN and offers new suggestions for the design of high-performance electrode materials for the ECRN.

Recent progress of Bi-based electrocatalysts for electrocatalytic CO2 reduction

To mitigate excessively accumulated carbon dioxide (CO₂) in the atmosphere and tackle the associated environmental concerns, green and effective approaches are necessary. The electrocatalytic CO₂ reduction reaction (CO₂RR) using sustainable electricity under benign reaction conditions represents a viable way to produce value-added and profitable chemicals. In this minireview, recent studies regarding unary Bi electrocatalysts and binary BiSn electrocatalysts are symmetrically categorized and reviewed, as they disclose high faradaic efficiencies toward the production of formate/formic acid, which has a relatively higher value of up to 0.50 $·per kg and has been widely used in the chemical and pharmaceutical industry. In particular, the preparation methodologies, electrocatalyst morphologies, catalytic performances and the corresponding mechanisms are comprehensively presented. The use of solid-state electrolytes showing high economic prospects for directly obtaining high-purity formic acid is highlighted. Finally, the remaining questions and challenges for CO₂RR exploitations using Bi-related electrocatalysts are proposed, while perspectives and the corresponding strategies aiming to enhance their entire catalytic functionalities and boost their performance are provided.

An industrial perspective on catalysts for low-temperature CO2 electrolysis

Electrochemical conversion of CO₂ to useful products at temperatures below 100 °C is nearing the commercial scale. Pilot units for CO₂ conversion to CO are already being tested. Units to convert CO₂ to formic acid are projected to reach pilot scale in the next year. Further, several investigators are starting to observe industrially relevant rates of the electrochemical conversion of CO₂ to ethanol and ethylene, with the hydrogen needed coming from water. In each case, Faradaic efficiencies of 80% or more and current densities above 200 mA cm^-2 can be reproducibly achieved. Here we describe the key advances in nanocatalysts that lead to the impressive performance, indicate where additional work is needed and provide benchmarks that others can use to compare their results.

Electrocatalysis for CO2 conversion: from fundamentals to value-added products

This timely and comprehensive review mainly summarizes advances in heterogeneous electroreduction of CO₂: from fundamentals to value-added products.

Continuous Electrochemical Reduction of CO2 to Formate: Comparative Study of the Influence of the Electrode Configuration with Sn and Bi-Based Electrocatalysts

Climate change has become one of the most important challenges in the 21st century, and the electroreduction of CO2 to value-added products has gained increasing importance in recent years. In this context, formic acid or formate are interesting products because they could be used as raw materials in several industries as well as promising fuels in fuel cells. Despite the great number of studies published in the field of the electrocatalytic reduction of CO2 to formic acid/formate working with electrocatalysts of different nature and electrode configurations, few of them are focused on the comparison of different electrocatalyst materials and electrode configurations. Therefore, this work aims at presenting a rigorous and comprehensive comparative assessment of different experimental data previously published after many years of research in different working electrode configurations and electrocatalysts in a continuous mode with a single pass of the inputs through the reactor. Thus, the behavior of the CO2 electroreduction to formate is compared operating with Sn and Bi-based materials under Gas Diffusion Electrodes (GDEs) and Catalyst Coated Membrane Electrodes (CCMEs) configurations. Considering the same electrocatalyst, the use of CCMEs improves the performance in terms of formate concentration and energy consumption. Nevertheless, higher formate rates can be achieved with GDEs because they allow operation at higher current densities of up to 300 mA·cm-2. Bi-based-GDEs outperformed Sn-GDEs in all the figures of merit considered. The comparison also highlights that in CCME configuration, the employ of Bi-based-electrodes enhanced the behavior of the process, increasing the formate concentration by 35% and the Faradaic efficiency by 11%.