Direct Electrochemical Conversion Research Articles

Direct Electrochemical Conversion of CO2 Sorbent Solution to Formate by a Molecular Iron Catalyst

Direct Electrochemical Conversion of CO₂ Sorbent Solution to Formate by a Molecular Iron Catalyst

Continuous Direct Air Capture and Electrochemical Conversion of CO2 and H2O into Ethylene and Oxygen in a Solid Electrolyte Reactor

Continuous Direct Air Capture and Electrochemical Conversion of CO₂ and H₂O into Ethylene and Oxygen in a Solid Electrolyte Reactor

Low-Temperature Electrochemical Oxidation of Methane into Alcohols

The direct oxidation of methane to methanol is considered challenging due to the intrinsically low reactivity of the C–H bond of methane and the formation of a large number of unstable intermediates (methanol, formaldehyde, and formic acid) relative to the yield of methane. However, promising advances have recently been reported in this area based on the use of electrochemical systems that differ from traditional thermal catalysis. In this review, the recent advances in direct and indirect electrochemical methane conversion with homogeneous catalysts are reviewed and discussed, especially under low-temperature conditions. Finally, the limitations of the current electrochemical methane conversion technology and future research directions are discussed.

Boosting CO2 electrocatalytic reduction to ethylene via hydrogen-assisted C-C coupling on Cu2O catalysts modified with Pd nanoparticles

Direct electrochemical conversion of CO2 to C2H4 is a promising technology for high-value chemical synthesis. However, challenges arise from competing hydrogen evolution reactions (HER) and the formation of undesired C1 products. In this study, we successfully engineered palladium nanoparticles (Pd NPs) with hydrogen storage capabilities on the Cu2O interface. This strategic modification effectively controls hydrogen states at the interface, leading to simultaneous HER inhibition and a significant increase in C2H4 selectivity. Detailed insights into the reaction mechanism were obtained through in-situ infrared spectroscopy, in-situ X-ray diffraction (XRD) and controlled experiments, offering a molecular-level understanding of the reaction mechanism. The interface-modified Pd NPs provided stable *H intermediates during the reaction process, effectively suppressing HER. Furthermore, the direct bonding between Pd and Cu interfaces increases charge density at the copper sites. These copper sites, in conjunction with the Pd-H sites, activate *CO at the Pd-Cu interface, forming stable *CHO intermediates. This enhances the coupling of *CHO and *CO intermediates, resulting in a remarkable increase in the C2H4/H2 production rate from 0.4 to 2.0 after Pd NPs modification, with a high faradaic efficiency of up to 46%. Our work presents a promising approach for designing copper-based CO2 reduction catalysts with outstanding activity and selectivity.

A minireview on electrochemical CO2 conversion based on carbonate/bicarbonate media

(Bi)Carbonate electrochemical conversion has emerged as a promising technology. Studies on mechanisms, along with latest progress in catalyst design and working electrode optimization. are summarized. Challenges and opportunities are also discussed.

In situ electrochemical regeneration of active 1,4-NADH for enzymatic lactic acid formation via concerted functions on Pt-modified TiO2/Ti.

Nicotinamide adenine dinucleotide (NAD+) and its reduced form (NADH) are key cofactors serving as essential hydrogen acceptors and donors to facilitate energy and material conversions under mild conditions. We demonstrate direct electrochemical conversion to achieve highly efficient regeneration of enzymatically active 1,4-NADH using a Pt-modified TiO2 catalyst grown directly on a Ti mesh electrode (Pt-TOT). Spectral analyses revealed that defects formed by the inclusion of Pt species in the lattice of TiO2 play a critical role in the regeneration process. In particular, Pt-TOT containing approximately 3 atom% of Pt exhibited unprecedented efficiency in the electrochemical reduction of NAD+ at the lowest overpotential to date. This exceptional performance led to the production of active 1,4-NADH with a significantly high yield of 86 ± 3% at -0.6 V vs. Ag/AgCl (-0.06 V vs. RHE) and an even higher yield of 99.5 ± 0.4% at a slightly elevated negative potential of -0.8 V vs. Ag/AgCl (-0.2 V vs. RHE). Furthermore, the electrochemically generated NADH was directly applied in the enzymatic conversion of pyruvic acid to lactic acid using lactate dehydrogenase.

Electrochemical C-H/C-C Bond Oxygenation: A Potential Technology for Plastic Depolymerization.

Herein, we provide eco-friendly and safely operated electrocatalytic methods for the selective oxidation directly or with water, air, light, metal catalyst or other mediators serving as the only oxygen supply. Heavy metals, stoichiometric chemical oxidants, or harsh conditions were drawbacks of earlier oxidative cleavage techniques. It has recently come to light that a crucial stage in the deconstruction of plastic waste and the utilization of biomass is the selective activation of inert C(sp3 )-C/H(sp3 ) bonds, which continues to be a significant obstacle in the chemical upcycling of resistant polyolefin waste. An appealing alternative to chemical oxidations using oxygen and catalysts is direct or indirect electrochemical conversion. An essential transition in the chemical and pharmaceutical industries is the electrochemical oxidation of C-H/C-C bonds. In this review, we discuss cutting-edge approaches to chemically recycle commercial plastics and feasible C-C/C-H bonds oxygenation routes for industrial scale-up.

Preparation and performance evaluation of low temperature SOEC using lithium compounds as electrodes

Previous studies have found that in ceramic fuel cells using Ni0·8Co0·15Al0·05LiO2 (NCAL) as the electrode, lithium compounds such as LiOH generated by reduction of NCAL anode by H2 diffuse into oxide electrolyte membranes such as Gd0.1Ce0·9O2 (GDC), and the “GDC-lithium compounds” composite electrolyte formed online is an excellent proton conductor. In this paper, the low-temperature electrolysis performance of proton conductor type solid oxide electrolysis cell (P-SOEC) with GDC as electrolyte and NCAL as electrode for direct electrochemical conversion of H2O into H2 was investigated. It is found that at operation temperature of 550 °C, the current density of the SOEC prepared in this paper can reach 2.263 A cm−2 at 1.6 V. The composite electrolyte in the electrolysis cell reaches an ionic conductivity of 0.572 S cm−1 in the SOEC mode. The excellent hydrogen production performance proves that this new type of electrolysis cell with lithium compounds as electrodes is a promising and potential proton conductive low-temperature SOEC.

(Invited) Green Ammonia-Mediated CO2 Capture and Direct Electrochemical Reduction to Formate

Direct electrochemical conversion of CO2 capture solutions (instead of gaseous CO2) into valuable chemicals can circumvent the energy-intensive CO2 regeneration and pressurization steps. While commonly used CO2 capture agents include alkali and amine solutions, ammonia has been rarely investigated. In another aspect, mismanagement of reactive nitrogen (Nr) in waste has emerged as a major problem in water pollution to our ecosystems, causing severe eutrophication and health concerns. Sustainably recovering Nr [such as nitrate (NO3 −)-N] and converting it into green ammonia (NH3) could mitigate the environmental impacts of Nr and reduce the NH3 demand from the carbon-intensive Haber-Bosch process, as well as a possible CO2 capture agent due to its alkaline nature.In this talk, we will present our rencet research on integration of electrodialysis and electrocatalysis for ammonia synthesis from dilute waste Nr sources, and green ammonia-mediated CO2 capture (to ammonium bicarbonate, NH4HCO3) and subsequent reduction to ammonium formate (NH4HCO2) as a new approach to CO2 capture and utilization (CCU). We have demonstrated a record-high NO3 −-to-NH3 performance in a scalable, versatile, and cost-effective membrane-free alkaline electrolyzer (MFAEL): an unprecedented NH3 partial current density of 4.22 ± 0.25 A cm−2 with a faradaic efficiency of 84.5 ± 4.9%. We also discovered that an ammonium bicarbonate (NH4HCO3)-fed electrolyzer with an anion exchange membrane (AEM) outperforms the state-of-the-art KHCO3 electrolyzer with a bipolar membrane (BPM) owing to its favorable thermal decomposition property, which allows for a 3-fold increase in the in situ CO2 concentration, a maximum 23% increase in formate faradaic efficiency, and a 35% reduction in cell voltage by substituting BPM with the AEM. Our integrated process by combining NH4HCO3 electrolysis with CO2 capturing by on-site generated green ammonia from the electro-reduction of nitrate in MFAEL has shown a remarkable 99.8% utilization of CO2 capturing agent. Such a multi-purpose process may offer a sustainable route for the simultaneous removal of Nr wastes and streamlined CO2 capturing and upgrading to valuable chemicals.

Understanding the dynamic evolution of atomically dispersed Cu catalyst for CO2 electrochemical conversion using integrated XANES analysis and mechanistic studies

Direct electrochemical conversion of CO2 to ethanol (CH3CH2OH) offers a promising strategy to lower CO2 emission while storing energy from renewable electricity. Our recent study reported a carbon-supported atomically dispersed Cu catalyst that achieved the highest reported selectivity for CH3CH2OH formation (91%) at a relatively low potential (-0.6 V), however, the active site structure that is responsible for such high activity and selectivity has yet to be understood. In this paper, we demonstrate a computational investigation combining X-ray absorption near edge structure (XANES) simulations and a mechanistic study via density functional theory (DFT) to understand the catalyst structures of this Cu catalyst during electrocatalysis and the corresponding reaction mechanisms of the key products. An integrated computational and experimental XANES analysis depicted the dynamic evolution of the catalytic site during electrocatalysis. The as-prepared, atomically dispersed Cu catalyst aggregates and forms metallic clusters/nanoparticles under electrochemical condition, which then break down to smaller oxidized clusters after electrocatalysis. The formed Cu clusters/nanoparticles showed distinct catalytic activity and selectivity as a function of particle size based on the mechanistic investigation using DFT, which is consistent with experimental observations for catalyst samples with different Cu loadings. This comprehensive study which combines experimental and computational XANES investigation, mechanistic study via DFT calculations, and experimental performance of the catalysts, provides unprecedented dynamic and mechanistic insights into the supported atomically dispersed metal catalysts for CO2 reduction. Such strategy and details gained can further guide discovery of novel catalyst materials for CO2 electrochemical reduction.

CO2 electroreduction to multicarbon products from carbonate capture liquid

CO2 electroreduction to multicarbon products from carbonate capture liquid

Harnessing dimethyl ether and methyl formate fuels for direct electrochemical energy conversion

In this work, the oxidation of a mixture of dimethyl ether (DME) and methyl formate (MF) was studied in both an aqueous electrochemical cell and a vapor-fed polymer electrolyte membrane fuel cell (PEMFC) utilizing a multi-metallic alloy catalyst, Pt3Pd3Sn2/C, discovered earlier by us. The current obtained during the bulk oxidation of a DME-saturated 1 M MF was higher than the summation of the currents provided by the two fuels separately, suggesting the cooperative effect of mixing these fuels. A significant increase in the anodic charge was realized during oxidative stripping of a pre-adsorbed DME + MF mixture as compared to DME or MF individually. This is ascribed to greater utilization of specific catalytic sites on account of the relatively lower adsorption energy of the dual- molecules than of the sum of the individual molecules as confirmed by the density functional theory (DFT) calculations. Fuel cell polarization was also conducted using a Pt3Pd3Sn2/C (anode) and Pt/C (cathode) catalysts-coated membrane (CCM). The enhanced surface coverage and active site utilization resulted in providing a higher peak power density by the DME + MF mixture-fed fuel cell (123 mW cm−2 at 0. 45 V) than with DME (84 mW cm−2 at 0.35 V) or MF (28 mW cm−2 at 0.2 V) at the same total anode hydrocarbon flow rate, temperature, and ambient pressure.

Tailoring *H Intermediate Coverage on the CuAl2O4/CuO Catalyst for Enhanced Electrocatalytic CO2 Reduction to Ethanol

AbstractThe direct electrochemical conversion of CO2 to multi‐carbon products offers a promising pathway for producing value‐added chemicals using renewable electricity. However, producing ethanol remains a challenge because of the competitive ethylene formation and hydrogen evolution reactions. Herein, we propose an active hydrogen (*H)‐intermediate‐mediating strategy for ethanol electroproduction on a layered precursor‐derived CuAl2O4/CuO catalyst. The catalyst delivered a Faradaic efficiency of 70 % for multi‐carbon products and 41 % for ethanol at current density of 200 mA cm−2 and exhibited a continuous 150 h durability in a flow cell. The intensive spectroscopic studies combined with theoretical calculations revealed that the in situ generated CuAl2O4 could tailor *H intermediate coverage and the elevated *H coverage favors the hydrogenation of the *HCCOH intermediate, accounting for the increased yield of ethanol. This work directs a pathway for enhancing ethanol electroproduction from CO2 reduction by tailoring *H intermediate coverage.

Tailoring *H Intermediate Coverage on the CuAl2 O4 /CuO Catalyst for Enhanced Electrocatalytic CO2 Reduction to Ethanol.

The direct electrochemical conversion of CO2 to multi-carbon products offers a promising pathway for producing value-added chemicals using renewable electricity. However, producing ethanol remains a challenge because of the competitive ethylene formation and hydrogen evolution reactions. Herein, we propose an active hydrogen (*H)-intermediate-mediating strategy for ethanol electroproduction on a layered precursor-derived CuAl2 O4 /CuO catalyst. The catalyst delivered a Faradaic efficiency of 70 % for multi-carbon products and 41 % for ethanol at current density of 200 mA cm-2 and exhibited a continuous 150 h durability in a flow cell. The intensive spectroscopic studies combined with theoretical calculations revealed that the in situ generated CuAl2 O4 could tailor *H intermediate coverage and the elevated *H coverage favors the hydrogenation of the *HCCOH intermediate, accounting for the increased yield of ethanol. This work directs a pathway for enhancing ethanol electroproduction from CO2 reduction by tailoring *H intermediate coverage.

Electrode configurations study for alkaline direct ethanol fuel cells

The direct electrochemical conversion of ethanol, a sustainable fuel, is an alternative sustainable technology of the future. In this study, membrane electrode assemblies with different electrode configurations for an alkaline direct ethanol fuel cell were fabricated and tested in a fuel cell device. The configurations include a catalyst-coated substrate (CCS), a catalyst-coated membrane (CCM), and a mixture of these two fabrication options. Two different anion exchange membranes were used to perform a comprehensive analysis. The fabricated CCSs and CCMs were characterized with single cell measurements, electro­chemical impedance spectroscopy and scanning electron microscopy. In addition, the swelling behavior of the membranes in alkaline solution was investigated in order to obtain information for CCM production. The results of the experimental electrochemical tests show that the CCS approach provides higher power densities (42.4 mW cm-2) than the others, regardless of the membrane type.

Direct electrochemical CO2 conversion using oxygen-mixed gas on a Cu network cathode and tailored anode.

Electrochemical CO2 reduction (eCO2R) by direct introduction of 60% air-containing CO2 mixed gas was demonstrated using a porous Cu network cathode formed on a hydrophobic gas diffusion layer (Cu/P-GDL). Cu/P-GDL exhibited eCO2R using the mixed gas with a remarkable faradaic efficiency of 85% for the production of C2+ chemicals, whereas a Cu cathode constructed on a conventional carbon gas diffusion layer (Cu/C-GDL) produced neither eCO2R products nor H2. Furthermore, the electrolyzer with Cu/P-GDL and optimized anode configuration achieved a partial current density of 132 mA cm-2 for C2+ chemicals even in the presence of 12% O2. Demonstration of eCO2R with impure CO2 gas would greatly expand its future applications.

Electrochemical conversion of lignin to short-chain carboxylic acids

A method for direct electrochemical conversion of lignin to short-chain carboxylic acids is developed.

The electrochemical study of NixCe1−xO2−δ electrodes using natural gas as a fuel

Solid oxide fuel cells (SOFCs) enable the direct electrochemical conversion of hydrocarbon-based fuels, such as natural gas, to electricity with high efficiency.

Techno-economic analysis and life-cycle assessment of the electrochemical conversion process with captured CO2 in an amine-based solvent

The assessment highlights the promise that direct electrochemical conversion of captured CO2 technology has the potential to be an economically and environmentally effective alternative to the current energy-demanding CO2 capture and utilization systems.

A tandem effect of atomically isolated copper-nitrogen sites and copper clusters enhances CO2 electroreduction to ethylene.

Direct electrochemical conversion of CO2 to C2H4 with high selectivity is highly desirable for lowering CO2 emissions. However, limited by the slow *CO dimerization step at a single active site, it is difficult for current electrocatalysts to further improve the selectivity toward C2H4. Here we report a tandem catalyst PDI-Cu/Cu with Cu-N sites and Cu clusters, synthesized by uniformly dispersing Cu clusters on a coordination polymer PDI-Cu, which has atomically isolated Cu-N sites. This tandem catalyst, which has an optimal content of Cu clusters, shows more than 2 times the enhancement in C2H4 production compared with that of the non-tandem catalyst PDI/Cu. Density functional theory (DFT) calculations support the tandem reaction mechanism, where Cu-N sites first reduce CO2 into highly concentrated CO and then the CO migrates to the surfaces of Cu clusters for further conversion into C2H4, decoupling the complex C2H4 generation pathway at single active sites into a two-step tandem reaction. This work offers a rational approach to design electrocatalysts for further boosting the selectivity of the CO2RR to C2+ products via a tandem route.