Oxygen-Resistant CO2 Reduction Enabled by Electrolysis of Liquid Feedstocks

Phase Transformation and Electrocatalytic CO2 Reduction in Ternary Au-Ag-Cu System

This study presents a two-step wet-chemistry method for synthesizing AuAgCux nanoparticles (NPs) using AuAg NP seeds. In-depth research investigates how composition and temperature interact to drive phase transformations, linking composition, structure, and catalytic function. These findings reveal that the alloying process exhibits unique composition-dependent behavior under heat treatment, resulting in a transformation sequence that progresses from a ternary alloy to a binary alloy, and ultimately to an ordered structure as composition varies. In this process, silver tends to migrate away from the stable AuAg alloy, diffusing outward to the surface, while copper diffuses inward, forming an AuCu alloy. CO2 reduction experiments demonstrate that the Faradaic efficiency of CO (FECO) can be finely tuned throughout the entire ternary system. Additionally, these results highlight the crucial roles of the AuCu phase and the density of grain boundaries (GB) in enhancing overall catalytic activity. This work not only sheds light on the complex interactions within ternary alloy systems but also provides valuable insights for designing more efficient electrochemical catalysts for CO2 reduction.

Mechanistic Insights Into H2O Dissociation in Overall Photo-/Electro-Catalytic CO2 Reduction

Photo-/electro-catalytic CO2 reduction with H2O to produce fuels and chemicals offers a dual solution to address both environmental and energy challenges. For a long time, catalyst design in this reaction system has primarily focused on optimizing reduction sites to improve the efficiency or guide the reaction pathway of the CO2 reduction half-reaction. However, less attention has been paid to designing activation sites for H2O to modulate the H2O dissociation half-reaction. Impressively, the rate-determining step in overall CO2 reduction is the latter, and it influences the evolution direction and formation energy of carbon-containing intermediates through the proton-coupled electron transfer process. Herein, we summarize the mechanism of the H2O dissociation half-reaction in modulating CO2 reduction performance based on cutting-edge research. These analyses aim to uncover the potential regulatory mechanisms by which H2O activation influences CO2 reduction pathways and conversion efficiency, and to establish a mechanism-structure-performance relationship that can guide the design and development of high-efficiency catalytic materials. A summary of advanced characterization techniques for investigating the dissociation mechanism of H2O is presented. We also discuss the challenges and offer perspectives on the future design of activation sites to improve the performance of photo-/electro-catalytic CO2 reduction.

Integrated Capture and Electrocatalytic Conversion of CO2: A Molecular Electrocatalysts Perspective

The ever-increasing concentration of atmospheric CO2, primarily driven by anthropogenic activities, has raised urgent environmental concerns, spurring the development of carbon capture and utilization (CCU) technologies. This review focuses on the integrated capture and electrochemical conversion of CO2 (ICECC), a promising approach that combines carbon capture with its direct electroreduction into value-added products. By eliminating energy-intensive steps such as CO2 release, compression, and transportation, ICECC offers a more energy-efficient and cost-effective alternative to conventional CCU methods. In this review, particular attention is given to molecular electrocatalysts, which offer high tunability and selectivity in electrochemical CO2 reduction reaction (eCO2RR). The role of capturing agents, including both external and dual-functional molecular systems, is critically examined to understand their influence on CO2 binding and catalytic efficiency. Whereas ICECC has significant potential, research in this area remains underexplored compared to conventional CO2 reduction methods. The review discusses the mechanistic insights into ICECC processes, highlighting key challenges and potential future research directions for improving catalyst design, enhancing capture efficiency, and scaling up ICECC technologies. These developments can make ICECC a critical component in achieving carbon neutrality and addressing climate change.

Minimizing Catalyst Loading for Efficient Electrolysis of Carbon Capture Solution to CO

Direct electrolysis of a CO2 absorption solution (i.e., bicarbonates solution) has emerged as a promising strategy for integrating carbon capture and utilization technologies, bypassing the need for CO2 recovery and pressurization processes prior to electrolysis. During the bicarbonate electrolysis, CO2 is generated in situ as bicarbonate reacts with protons from the membrane within an electrolyzer, resulting in higher CO2 utilization efficiency compared to conventional CO2 electrolysis. However, the high loadings of precious metal catalyst, typically around 4.0 mg cm-2, represent a significant limitation. Herein, we utilized a cost-effective flame spray pyrolysis (FSP) technique to deposit silver nanoparticles (AgNPs) onto carbon cloth, followed by coating of commercial AgNPs (Cml-AgNPs). Benefiting from high surface area and uniform coverage, the cathode with FSP + Cml-AgNPs achieves comparable CO selectivity with only one-third of the AgNPs loading required for conventional airbrush deposition. Leveraging the high catalyst performance and uniform particle dispersion of FSP, this electrode preparation method presents a scalable and economical solution for bicarbonate electrolysis and electrochemical CO2 conversion.

Towards the Use of Low-Concentration CO2 Sources by Direct Selective Electrocatalytic Reduction

The direct CO2 reduction reaction (CO2RR) from simulated flue gas of various CO2 concentrations could minimize extra energy for pre-concentration processes to highly concentrated CO2 as a feedstock. We investigate the challenges for CO2RR caused by low CO2 concentrations and provide strategies concerning the impact of the chosen electrocatalyst material and the selection of the electrolyte to attain high CO selectivity. We continuously feed CO2 mixed with N2 (the typical dilutant in flue gas) in various ratios to gas diffusion electrodes in a model flow-through electrolyzer. Operating the CO2RR at lower CO2 concentrations results in an overpotential shift to more cathodic values. We show that higher active catalysts can maintain high CO selectivity down to 5 % CO2 by using NiCu-based catalysts. NiCu reached its limit when the CO2 concentration was lowered to 2 %, due to low CO2 availability and competition of carbonate formation. Employing near-neutral electrolytes with buffering capacity, we maintained high Faradaic efficiency at low overpotentials and higher CO2 utilization at low CO2 concentration.

Electrochemical valorization of captured CO2: recent advances and future perspectives

The excessive emission of CO2 has led to severe climate change, prompting global concern. Capturing CO2 and converting it through electrochemistry into value-added products represent promising approaches to mitigating CO2 emissions and closing the carbon cycle. Traditionally, these two processes have been performed independently, involving multiple steps, high energy consumption, and low efficiency. Recently, the electrochemical conversion of captured CO2, which integrates the capture and conversion processes (also referred to as electrochemically reactive CO2 capture), has garnered increasing attention. This integrated approach bypasses the energy-intensive steps involved in the traditional independent process, including CO2 release, purification, compression, transportation, and storage. In this review, we discuss recent advances in the electrochemical conversion of captured CO2, focusing on four key aspects. First, we introduce various capture media, emphasizing the thermodynamic aspects of carbon capture and their implications for integration with electrochemical conversion. Second, we discuss product control mediated by the selection of different catalysts, highlighting the connections between the conversion of captured CO2 and gas-fed CO2. Third, we examine the effect of reactor systems and operational conditions on the electrochemical conversion of captured CO2, shedding light on performance optimization. Finally, we explore real integration systems for CO2 capture and electrochemical conversion, revealing the potential of this new technology for practical applications. Overall, we provide insights into the existing challenges, potential solutions, and thoughts on opportunities and future directions in the emerging field of electrochemical conversion of captured CO2.

Reactive carbon capture using electrochemical reactors

The electrolytic upgrading of CO2 presents a promising strategy to mitigate global CO2 emissions while generating valuable carbon-based products such as carbon monoxide, formate, and ethylene. However, the adoption of industrial-scale CO2 electrolyzers is hindered by the high energy and capital costs associated with the purification and pressurization of captured CO2 prior to electrolysis. One promising solution is "reactive carbon capture," which involves the electrolytic conversion of the eluent from CO2 capture units, or the "reactive carbon solution," directly into valuable products. This approach circumvents the energy-intensive processes required for electrolyzers fed with gaseous CO2. This Tutorial Review highlights recent advances for reactive carbon capture, showcasing its potential as a scalable solution for electrolyzers that upgrade CO2 into fuels and products.

Reactive Carbon Capture Enables CO2 Electrolysis with Liquid Feedstocks

ConspectusThe electrochemical reduction of carbon dioxide (CO2RR) is a promising strategy for mitigating global CO2 emissions while simultaneously yielding valuable chemicals and fuels, such as CO, HCOO-, and C2H4. This approach becomes especially appealing when integrated with surplus renewable electricity, as the ensuing production of fuels could facilitate the closure of the carbon cycle. Despite these advantages, the realization of industrial-scale electrolyzers fed with CO2 will be challenged by the substantial energy inputs required to isolate, pressurize, and purify CO2 prior to electrolysis.To address these challenges, we devised an electrolyzer capable of directly converting reactive carbon solutions (e.g., a bicarbonate-rich eluent that exits a carbon capture unit) into higher value products. This "reactive carbon electrolyzer" operates by reacting (bi)carbonate with acid generated within the electrolyzer to produce CO2 in situ, thereby facilitating CO2RR at the cathode. This approach eliminates the need for expensive CO2 recovery and compression steps, as the electrolyzer can then then coupled directly to the CO2 capture unit.This Account outlines our endeavors in developing this type of electrolyzer, focusing on the design and implementation of materials for electrocatalytic (bi)carbonate conversion. We highlight the necessity for a permeable cathode that allows the efficient transport of (bi)carbonate ions while maintaining a sufficiently high catalytic surface area. We address the importance of the supporting electrolyte, detailing how (bi)carbonate concentration, counter cations, and ionic impurities impact selectivity for products formed in the electrolyzer. We also catalog state-of-the-art performance metrics for reactive carbon electrolyzers (i.e., Faradaic efficiency, full cell voltage, CO2 utilization efficiency) and outline strategies to bridge the gap between these values and those required for commercial operation Collectively, these findings contribute to the ongoing efforts to realize industrial-scale electrochemical reactors for CO2 conversion, bringing us closer to a sustainable and closed-loop carbon cycle.