Electrochemical Reduction Of CO2 Research Articles

Corrosion and Enhanced Hydrogen Evolution in Electrochemical Reduction of Ammonium Carbamate on Transition Metal Surfaces.

Experiments and theory are combined to search for catalyst activity and stability descriptors for the direct reactive capture and conversion (RCC) of CO2 in ammonia capture solutions using Cu, Ag, Au, Sn, and Ti electrodes. Two major phenomena emerge in RCC that are not predominant in the electrochemical CO2 reduction (CO2R) reaction, namely, the rapid corrosion and restructuring of the catalyst in the presence of the CO2-ammonia adducts and the promotion of the competing hydrogen evolution reaction (HER). The prevalence of HER in RCC is correlated to the electrostatic attraction of the protonated amine to the electrode and the repulsion of the captured CO2, using the potential of zero charge (PZC). The stability of catalysts under RCC conditions is a function of the applied potential and cannot be readily predicted using binding energy descriptors commonly used in the prediction of CO2R activity. A direct correlation between calculated binding energies of CO2R intermediates, atomic oxygen, hydrogen, and ammonia and the activity and stability of transition metals for RCC cannot be found, highlighting the need for descriptors beyond those known for CO2R.

Hierachical Aerogel-Supported Cu-Sn-Ox Solid Solutions for Highly Selective CO2 Electroreduction and Zn-CO2 Batteries.

The electrochemical CO2 reduction reaction (CO2RR) into high-value carbon compounds such as CO and HCOOH is a promising strategy for the utilization and conversion of emitted CO2. However, the selectivity of the CO2RR for HCOOH is typically less than 90% and operates within a narrow voltage range, which limits its practical application. Herein, we propose a novel heterostructural aerogel as a highly efficient electrocatalyst for CO2RR to HCOOH. This catalyst consists of Cu-Sn-Ox solid solutions embedded in a reduced graphene oxide matrix (Cu-Sn-Ox/rGO). The incorporation of Cu2+ into the SnO2 matrix enhances HCOOH production by improving the adsorption of the *OCHO intermediate and inhibiting H2 evolution, as confirmed by in situ measurements and computational studies. As a result, Cu-Sn-Ox/rGO achieves a remarkable Faradaic efficiency (FE) of up to 91.4% for HCOOH and maintains high selectivity over a broad operating voltage range (-0.8 to -1.1 V). Additionally, the assembled Zn-CO2 batteries demonstrated an excellent power density of 1.14 mW/cm2 and exceptional stability for over 25 h.

One-pot hydrothermal synthesis of transition metal sulfides-decorated CuS microflower-like structures for electrochemical CO2 reduction to CO

Electrochemical CO2 reduction (ECR) to value-added products is regarded as a sustainable strategy to mitigate global warming and energy crisis, and designing highly efficient and robust catalysts is essential. In this work, transition metal sulfides (TMS)-decorated CuS microflower-like structures were prepared via the one-pot hydrothermal synthesis method for ECR to CO, and the influence of TMS doping on ECR performance was demonstrated. Characterization of the catalysts was performed using XRD, FESEM-EDS, N2 physisorption, and XPS, revealing the successful loading of TMS, the formation of microflower-like architectures and the generation of sulfur vacancies. Electrochemical tests demonstrated that doping ZnS, Bi2S3, CdS and MoS2 improved the intrinsic CO2 reduction activity of the CuS catalyst. Particularly, the MoS2-CuS composite catalyst with imperfect petal-like structure showed uniform distribution of edge Mo sites, which worked synergistically with the formed grain boundaries (GBs) and undercoordinated S vacancy sites in promoting CO2 activation, stabilizing *COOH adsorption, facilitating *CO desorption, and lowering the energy barrier of the potential-limiting step for improved CO selectivity. The MoS2-CuS catalyst achieved a maximum CO selectivity of 83.2% at –0.6 V versus the reversible hydrogen electrode (RHE) and a high CO cathodic energetic efficiency of 100%. At this potential, the catalyst maintained stable catalytic activity and CO selectivity during a 333-min electrolysis process. The findings will offer a promising avenue for the development of efficient and stable catalysts for CO production from ECR.

Electrocatalysis of CO2 Reduction by Immobilized Formate Dehydrogenase without a Metal Redox Center.

Nicotinamide adenine dinucleotide-dependent formate dehydrogenase from Candida boidinii was immobilized in a 1,2-dimyristoyl-sn-glycero-3-phosphocholine/cholesterol floating lipid bilayer on the gold surface as a biocatalyst for electrochemical CO2 reduction. We report that, in contrast to common belief, the enzyme can catalyze the electrochemical reduction of CO2 to formate without the cofactor protonated nicotinamide adenine dinucleotide. The electrochemical data indicate that the enzyme-catalyzed reduction of CO2 is diffusion-controlled and is a reversible reaction. The orientation and conformation of the enzyme were investigated by surface-enhanced infrared reflection absorption spectroscopy. The α-helix of the enzyme adopts an orientation nearly parallel to the surface, bringing its active center close to the gold surface. This orientation allows direct electron transfer between CO2 and the gold electrode. The results in this paper provide a new method for the development of enzymatic electrocatalysts for CO2 reduction.

Sr(Ti0·3Fe0.7)O3−δ-based perovskite with in-situ exsolved Fe–Ru nanoparticles: A highly stable fuel electrode material for solid oxide electrochemical cells with efficient electrocatalytic CO2 reduction ability and preferential selectivity

The development of solid-oxide cells requires fuel electrodes capable of promoting highly catalytic activities for CO2 electrochemical reduction (CO2R). This study develops a fuel electrode material, Sr(Ti0·3Fe0·63Ru0.07)O3-δ (STFR) perovskite, enhance with in-situ exsolved Fe–Ru nanoparticles (STFR–FeRu), demonstrating excellent electrochemical catalytic activity for CO2R, considerable stability, and high selectivity for CO2 electrolysis. Notably, the study discovered for the first time that STFR–FeRu exhibits significantly enhanced catalytic activity in a CO2-containing atmosphere compares to that in hydrogen-based fuels. At 800 °C and 1.3 V, La0·8Sr0.2Ga0.8Mg0·2O3-δ electrolyte-supported cells with STFR–FeRu fuel electrode, for direct CO2 electrolysis, realizes a current density of 1.77 A cm−2. This current density is 50 % higher than that of H2O electrolysis under the same conditions. Additionally, the cell achieves a current density of 1.54 A cm−2 for CO2–H2O co-electrolysis, with a high CO2 electrolysis selectivity (CO concentration exceeding 60 % in the electrolysis products).

Charge transfer regulates electrocatalytic CO2 reduction on one-dimensional carbon nanotube/boron nitride nanotube heterostructures

Driving the electrochemical carbon dioxide reduction reaction (CO2RR) to generate high-value chemicals is one of the effective solutions to promote carbon–neutral cycles. Herein, we use a heterostructure strategy to enhance the catalytic performance of single-atom catalysts (SACs) for CO2RR. A series of catalysts formed by doping some transition metal atoms (TM = Cr, Mn, Fe, Co, Ni, Cu) into heterostructures which include the single-wall carbon nanotube in boron nitride nanotube (CNT@BNNT) and the hybridization of carbon nanotube and boron nitride nanotube (CNT/BNNT) are respectively named as TM-CNT@BNNT and TM-CNT/BNNT, and their catalytic activity of CO2RR is systematically studied using density functional theory methods. After forming a heterostructure, the number of charges transferred from the metal center to the substrate and the d-band center will change, which will, to some extent, regulate the catalytic activity of the catalyst. Due to the effective activation of CO2 and significant inhibition ability of competitive hydrogen evolution reaction, nine catalysts are considered effective candidates for CO2RR. Finally, seven catalysts with high CO2RR activity are selected by calculating the Gibbs free energy. The moderate linear relations between charge transfer and adsorption energy of CO2/free energy change of reaction intermediates/limiting potential indicate that charge transfer can regulate activity to a certain extent. The improvement of CO2RR activity comes from the smaller charge transfer in the metal center, which is more likely to result in moderate binding strength between the catalyst and the key intermediate (*OH) to generate high catalytic performance.

Reaction mechanism of metal-free borophene catalyst electrochemical reduction of CO2

The utilization of electricity generated from renewable energy sources for carbon dioxide reduction reaction (CO2RR) to produce high-value chemical resources is of significant importance for reducing CO2 emissions and for energy storage. However, the search for environmentally friendly and efficient metal-free catalysts to facilitate CO2 conversion continues to present numerous challenges. This study employs density functional theory (DFT) calculation to explore the potential of two-dimensional metal-free borophene catalysts in the activation and conversion of CO2. Through molecular dynamics simulations, energy band and density of states analysis, the stability and electronic properties of metal-free borophene were thoroughly examined. The calculations demonstrated that two specific sites on electron-deficient zigzag borophene possess strong adsorption capabilities for CO2, enabling effective activation of CO2. Further investigation revealed that the reduction of CO2 at site 1 on zigzag borophene efficiently produces CO, HCOOH, CH3OH, and CH4, with the potential determining steps (PDS) requiring overpotentials of 0.11 V, 0.20 V, 0.38 V, and 0.52 V, respectively. In summary, this research provides theoretical foundation for the use of metal-free borophene as an efficient catalyst for CO2RR.

Electrolyte Composition-Dependent Product Selectivity in CO2 Reduction with a Porphyrinic Metal-Organic Framework Catalyst.

A copper porphyrin-derived metal-organic framework electrocatalyst, FICN-8, was synthesized and its catalytic activity for CO2 reduction reaction (CO2RR) was investigated. FICN-8 selectively catalyzed electrochemical reduction of CO2 to CO in anhydrous acetonitrile electrolyte. However, formic acid became the dominant CO2RR product with the addition of a proton source to the system. Mechanistic studies revealed the change of major reduction pathway upon proton source addition, while catalyst-bound hydride (*H) species was proposed as the key intermediate for formic acid production. This work highlights the importance of electrolyte composition on CO2RR product selectivity.

Dynamic Cation Enrichment during Pulsed CO2 Electrolysis and the Cation-Promoted Multicarbon Formation.

Recently, pulsed electrolysis has been demonstrated as an emerging electrochemical technique that significantly promotes the performance of various electrocatalysis applications. The ionic nature of aqueous electrolytes implies a likely change in ionic distribution under these alternating potential conditions. However, despite the well-known importance of cations, the impact of pulsed electrolysis on the cation distribution remains unexplored as well as its influences on the performance. Herein, we explore the cation effects on the pulsed electrochemical CO2 reduction (p-CO2RR) using the most widely utilized alkali metal cations, including Li+, Na+, K+, and Cs+. It is discovered that the nature of cations can significantly influence the product ratio of C2+ over C1 (mostly CH4) during p-CO2RR in an order of Li+< Na+< K+< Cs+, much more profoundly than those of static cases. We report direct experimental evidence for the cation enrichment caused by pulsed electrolysis, depending on the radius of the hydrated ions. With further quasi-in situ analysis of the catalyst surface, the cation-promoted Cu dissolution-and-redeposition process was identified; this is found to alter the surface CuxO/Cu ratio during the pulsed process. We demonstrate that both the cation enrichment and the cation-adjusted surface CuxO/Cu composition impact the C2+/C1 ratio through the control of the surface-adsorbed CO population. These results reveal the presence of pulse-induced cation redistribution in emerging pulsed electrolysis techniques and provide a comprehensive understanding of alkali metal cation effects for improving the selectivity of p-CO2RR.

Ligand-tuning copper in coordination polymers for efficient electrochemical C–C coupling

Cu catalyses electrochemical CO2 reduction to valuable multicarbon products but understanding the structure-function relationship has remained elusive due to the active Cu sites being heterogenized and under dynamic re-construction during electrolysis. We herein coordinate Cu with six phenyl-1H-1,2,3-triazole derivatives to form stable coordination polymer catalysts with homogenized, single-site Cu active sites. Electronic structure modelling, X-ray absorption spectroscopy, and ultraviolet–visible spectroscopy show a widely tuneable Cu electronics by modulating the highest occupied molecular orbital energy of ligands. Using CO diffuse reflectance Fourier transform infrared spectroscopy, in-situ Raman spectroscopy, and density functional theory calculations, we find that the binding strength of *CO intermediate is positively correlated to highest occupied molecular orbital energies of the ligands. As a result, we enable a tuning of C–C coupling efficiency—a parameter we define to evaluate the efficiency of C2 production—in a broad range of 0.26 to 0.86. This work establishes a molecular platform that allows for studying structure-function relationships in CO2 electrolysis and devises new catalyst design strategies appliable to other electrocatalysis.

Low-temperature fabrication of morphology-controllable Cu2O for electrochemical CO2 reduction

Cu2O has been successfully synthesized in different morphologies/sizes (nanoparticles and octahedrons) via a low-temperature chemical reduction method. Trapping metal ions in an ice cube and letting them slowly melt in a reducing agent solution is the simplest way to control the nanostructure. Enhancement of charge transfer and transportation of ions by Cu2O nanoparticles was shown by cyclic voltammetry and electrochemical impedance spectroscopy measurements. In addition, nanoparticles exhibited higher current densities, the lowest onset potential, and the Tafel slope than others. The Cu2O electrocatalyst (nanoparticles) demonstrated the Faraday efficiencies (FEs) of CO, CH4, and C2H6 up to 11.90, 76.61, and 1.87%, respectively, at −0.30 V versus reference hydrogen electrode, which was relatively higher FEs than other morphologies/sizes. It is mainly attributed to nano-sized, more active sites and oxygen vacancy. In addition, it demonstrated stability over 11 h without any decay of current density. The mechanism related to morphology tuning and electrochemical CO2 reduction reaction was explained. This work provides a possible way to fabricate the different morphologies/sizes of Cu2O at low-temperature chemical reduction methods for obtaining the CO, CH4, and C2H6 products from CO2

Amorphous Nanomaterials: Emerging Catalysts for Electrochemical Carbon Dioxide Reduction

AbstractIn the past decades, the rapid depletion of non‐renewable energy sources has caused growing energy crisis and increasing emissions of carbon dioxide (CO2), which aggravates global warming and catastrophic climate change. Electrocatalysis is regarded as an effective method for consuming atmospheric CO2 and simultaneously alleviating the energy problem by converting CO2 into high value‐added chemicals. Amorphous nanomaterials with long‐range disordered structures possess abundant highly unsaturated atomic sites and dangling bonds on their surfaces, thus providing a large number of active sites, and show unique electronic structures compared to their crystalline counterparts due to the distinct atomic arrangements. Therefore, amorphous nanomaterials are recently demonstrated as highly efficient catalysts for diverse electrocatalytic reactions, including electrocatalytic CO2 reduction reaction (CO2RR). Here the rational synthesis and electrocatalytic performance of newly emerging amorphous nanomaterials will be outlined for electrocatalytic CO2RR. Importantly, the intrinsic merits of these amorphous catalysts in CO2RR processes will be summarized and highlighted. Finally, these perspectives on the remaining challenges and some potential future directions in this emerging field will also be provided.

Zn-Cu bimetallic gas diffusion electrodes for electrochemical reduction of CO2 to ethylene

The application of renewable energy to drive the electroreduction of carbon dioxide (CO2) into valuable compounds serves as a means of energy storage and simultaneously aids in the mitigation of climate change. In this study, a bimetallic catalyst consisting of Zinc and Copper is synthesized using the Zinc-doped HKUST-1 metal-organic framework. The catalyst is then fabricated on gas diffusional electrode and investigated in both H-Cell and Flow cell configurations for electrochemical CO2 reduction reaction (ECO2RR). In the H-Cell, the catalysts that have been developed exhibit an ethylene faradaic efficiency (FE) up to 40 % when operated at a potential of −0.8 V relative to the reversible hydrogen electrode (RHE). The Zn-Cu bimetallic gas diffusion electrodes (GDE) exhibit an impressive ethylene FE up to 45 % when operating at a current density of −200 mA cm−2 at −1.0 V versus RHE in the flow cell. This research offers valuable insights into the strategic development of copper-based bimetallic catalysts with the aim of enhancing the efficiency of electrochemical reduction of CO2 to yield multicarbon compounds.

Electronic perturbation of Cu nanowire surfaces with functionalized graphdiyne for enhanced CO2 reduction reaction

Abstract Electronic perturbation of Cu catalysts surface is crucial for optimizing electrochemical CO2 reduction activity, yet still poses great challenges. Herein, nanostructured Cu nanowires (NW) with fine-tuned surface electronic structure are achieved via surface encapsulation with electron-withdrawing (–F) and -donating (–Me) group-functionalized graphdiynes (R-GDY, R = –F and –Me), and the resulting catalysts, denoted as R-GDY/Cu NW, display distinct CO2 reduction performances. In-situ electrochemical spectroscopy revealed that the *CO (a key intermediate of the CO2 reduction reaction) binding affinity and consequent *CO coverage positively correlate to the Cu surface oxidation state, leading to the favorable C–C coupling on F-GDY/Cu NW over Me-GDY/Cu NW. Electrochemical measurements corroborate the favorable C2H4 production with an optimum C2+ selectivity of 73.15% ± 2.5% observed for F-GDY/Cu NW, while the predominant CH4 production is favored by Me-GDY/Cu NW. Furthermore, leveraging the *Cu–OH/*CO ratio as a descriptor, mechanistic investigation reveals that the protonation of distinct adsorbed *CO facilitated by *Cu–OH is crucial for the selective generation of C2H4 and CH4 on F-GDY/Cu NW and Me-GDY/Cu NW, respectively.

Stable Cu+/Cu2+ species derived from in-situ growing Cu-S-V bonds in CuVxS electrocatalysts enables high efficiency CO2 electroreduction to methanol

Regulating oxidation state of Cu-based chalcogenides catalysts during electrolysis is of great significance for efficient CO2 electrochemical reduction reaction (CO2RR) to methanol, which still remains a dramatic challenge. Herein, we construct a heterogeneous Cu3VS4/CuS electrocatalyst (denoted as CuVxS), in which the in-situ growing Cu-S-V bonds avoid the accumulated electrons on oxidized Cu sites and inhibit the deep reduction of CuS to metallic Cu during electrolysis, maintaining stable and abundant reactive Cu+/Cu2+ species to promote CO2RR performance to methanol. By this design, the CuV0.1S catalyst achieves an ultrahigh methanol selectivity of 79.8 %. In-situ FTIR measurement reveals that the synergistic effect of Cu+/Cu2+ species and Cu-S-V bonding facilitates the *CO adsorption and the subsequent *CO hydrogenation process, which improve the generation of *CHO and *OCH3 intermediates for enhanced methanol selectivity. This work provides a new insight into stabilizing high oxidation state of Cu-based electrocatalyst to maintain sufficient active sites for CO2RR.

Oxygen Vacancy-Driven Heterointerface Breaks the Linear-Scaling Relationship of Intermediates toward Electrocatalytic CO2 Reduction.

Smart metal-metal oxide heterointerface construction holds promising potentials to endow an efficient electron redistribution for electrochemical CO2 reduction reaction (CO2RR). However, inhibited by the intrinsic linear-scaling relationship, the binding energies of competitive intermediates will simultaneously change due to the shifts of electronic energy level, making it difficult to exclusively tailor the binding energies to target intermediates and the final CO2RR performance. Nonetheless, creating specific adsorption sites selective for target intermediates probably breaks the linear-scaling relationship. To verify it, Ag nanoclusters were anchored onto oxygen vacancy-rich CeO2 nanorods (Ag/OV-CeO2) for CO2RR, and it was found that the oxygen vacancy-driven heterointerface could effectively promote CO2RR to CO across the entire potential window, where a maximum CO Faraday efficiency (FE) of 96.3% at -0.9 V and an impressively high CO FE of over 62.3% were achieved at a low overpotential of 390 mV within a flow cell. The experimental and computational results collectively suggested that the oxygen vacancy-driven heterointerfacial charge spillover conferred an optimal electronic structure of Ag and introduced additional adsorption sites exclusively recognizable for *COOH, which, beyond the linear-scaling relationship, enhanced the binding energy to *COOH without hindering *CO desorption, thus resulting in the efficient CO2RR to CO.

Modulating the coordination environment and metal choice in carbon buckypapers supported metal phthalocyanines for enhanced electrocatalytic carbon dioxide reduction

In the search of versatile electrocatalysts for the electrochemical reduction of carbon dioxide (CO2RR), different transition metal phthalocyanines (MPc, where M=Fe, Co, Ni and Cu) have been immobilized by an easy and scalable wet impregnation on carbon nanotubes (CNTs) in the form of buckypaper (BP). Both the nature of the metal and the surface chemistry of the carbon support were found to play a pivotal role in determining their CO2RR efficiency and selectivity. We disclose here a potentiodynamic strategy for the controlled surface modification of BP with N- and P-containing polymeric species as a simple heterogenization strategy for molecular catalysts, enabling to easily tune their electrocatalytic performance. Syngas (mixture of H2 and CO) was obtained as the main product from CO2RR using FePc, CoPc and NiPc as electrocatalysts on functionalized (BPf) or non-modified BP. In contrast, CuPc was found to mainly catalyze the hydrogen evolution reaction (HER), with small amounts of formate as the only CO2RR product. It is possible to modulate the H2/CO ratio in the final product through the appropriate selection of the metal in MPc, the modification of the coordination environment by the controlled functionalization of the carbon support and the adjustment of the operating conditions. In particular, H2/CO ratios in a range between 0.17 and 1.28 have been obtained with good stability during electrolysis. Among all the MPc studied, CoPc surfaced as the most promising candidate for the reduction of CO2 to CO and H2 production, a finding substantiated by computational studies highlighting the positive impact of phosphate ligands on CoPc. This strategy outlines the starting line of a potential route toward the controlled generation of CO2RR-related products.

Deconvoluting XPS Spectra of La-Containing Perovskites from First-Principles.

Perovskite-based oxides are used in electrochemical CO2 and H2O reduction in electrochemical cells due to their compositional versatility, redox properties, and stability. However, limited knowledge exists on the mechanisms driving these processes. Toward this understanding, herein we probe the core level binding energy shifts of water-derived adspecies (H, O, OH, H2O) as well as the adsorption of CO2 on LaCoO3 and LaNiO3 and correlate the simulated peaks with experimental temperature-programmed X-ray photoelectron spectroscopy (TPXPS) results. We find that the strong adsorption of such chemical species can affect the antiferromagnetic ordering of LaNiO3. The adsorption of such adspecies is further quantified through Bader and differential charge analyses. We find that the higher O 1s core level binding energy peak for both LaCoO3 and LaNiO3 corresponds to adsorption of water-related species and CO2, while the lower energy peak is due to lattice oxygen. We further correlate these density functional theory-based core level O 1s binding energies with the TPXPS measurements to quantify the decrease of the O 1s contribution due to desorption of adsorbates and the apparent increase of the lattice oxygen (both bulk and surface) with temperature. Finally, we quantify the influence of adsorbates on the La 4d, Co 2p, and the Ni 3p core level binding energy shifts. This work demonstrates how theoretically generated XPS data can be utilized to predict species-specific binding energy shifts to assist in deconvolution of the experimental results.

Amphipathic Surfactant on Reconstructed Bismuth Enables Industrial-Level Electroreduction of CO2 to Formate.

Developing efficient electrocatalysts for selective formate production via the electrochemical CO2 reduction reaction (CO2RR) is challenged by high overpotential, a narrow potential window of high Faradaic efficiency (FEformate), and limited current density (Jformate). Herein, we report a hierarchical BiOBr (CT/h-BiOBr) with surface-anchored cetyltrimethylammonium bromide (CTAB) for formate-selective large-scale CO2RR electrocatalysis. CT/h-BiOBr achieves over 90% FEformate across a wide potential range (-0.5 to -1.1 V) and an industrial-level Jformate surpassing 100 mA·cm-2 at -0.7 V. In situ investigations uncover the reconstructed Bi(110) surface as the active phase, with CTAB playing a dual role: its hydrophobic alkyl chains create a CO2-enriching microenvironment, while its polar head groups fine-tune the electronic structure, fostering a highly active phase. This work provides valuable insights into the role of surfactants in electrocatalysis and guides the design of electrocatalysts for the large-scale CO2RR.

Direct quantification of electrochemical CO2 reduction products with an improved DEMS setup

Direct quantification of electrochemical CO2 reduction products with an improved DEMS setup