Electrocatalysts For CO Research Articles

Electrochemical CO2 Reduction via Low-Valent Nickel Single-Atom Catalyst

Electrochemical conversion of CO 2 to CO with high intrinsic activity, selectivity, and stability was demonstrated on a low-valent Ni single-atom catalyst. The nature of catalytic sites and their evolutions under catalytic condition were identified, which should provide important guidance toward building efficient electrocatalysts for CO 2 reduction.

Design of Single-Atom Co-N5 Catalytic Site: A Robust Electrocatalyst for CO2 Reduction with Nearly 100% CO Selectivity and Remarkable Stability.

We develop an N-coordination strategy to design a robust CO2 reduction reaction (CO2RR) electrocatalyst with atomically dispersed Co-N5 site anchored on polymer-derived hollow N-doped porous carbon spheres. Our catalyst exhibits high selectivity for CO2RR with CO Faradaic efficiency (FECO) above 90% over a wide potential range from -0.57 to -0.88 V (the FECO exceeded 99% at -0.73 and -0.79 V). The CO current density and FECO remained nearly unchanged after electrolyzing 10 h, revealing remarkable stability. Experiments and density functional theory calculations demonstrate single-atom Co-N5 site is the dominating active center simultaneously for CO2 activation, the rapid formation of key intermediate COOH* as well as the desorption of CO.

Hydronium-Induced Switching between CO2 Electroreduction Pathways.

Over a broad range of operating conditions, many CO2 electroreduction catalysts can maintain selectivity toward certain reduction products, leading to materials and surfaces being categorized according to their products; here we ask, is product selectivity truly a property of the catalyst? Silver is among the best electrocatalysts for CO in aqueous electrolytes, where it reaches near-unity selectivity. We consider the hydrogenations of the oxygen and carbon atoms via the two proton-coupled-electron-transfer processes as chief determinants of product selectivity; and find using density functional theory (DFT) that the hydronium (H3O+) intermediate plays a key role in the first oxygen hydrogenation step and lowers the activation energy barrier for CO formation. When this hydronium influence is removed, the activation energy barrier for oxygen hydrogenation increases significantly, and the barrier for carbon hydrogenation is reduced. These effects make the formate reaction pathway more favorable than CO. Experimentally, we then carry out CO2 reduction in highly concentrated potassium hydroxide (KOH), limiting the hydronium concentration in the aqueous electrolyte. The product selectivity of a silver catalyst switches from entirely CO under neutral conditions to over 50% formate in the alkaline environment. The simulated and experimentally observed selectivity shift provides new insights into the role of hydronium on CO2 electroreduction processes and the ability for electrolyte manipulation to directly influence transition state (TS) kinetics, altering favored CO2 reaction pathways. We argue that selectivity should be considered less of an intrinsic catalyst property, and rather a combined product of the catalyst and reaction environment.

Synthesis of heterometallic metal-organic frameworks and their performance as electrocatalyst for CO2 reduction.

Herein we report the solventless synthesis and doping of the benchmark HKUST-1(Cu) as a facile route to afford heterometallic metal–organic frameworks (MOFs) having proficient behavior as electrocatalytic materials in the reduction of carbon dioxide. Zn(ii), Ru(iii) and Pd(ii) were selected as doping metals (MD) with the aim of partially replacing the Cu(ii) atoms of the pristine structure to afford HKUST-1(Cu,MD) type materials. Apart from the high yield and good crystallinity of the obtained materials, the extremely high reagent concentration that the reaction conditions imply makes it feasible to control dopant loading in all cases. Prepared samples were processed as electrodes and assembled in a continuous flow filter-press electrochemical cell. Faraday efficiency to methanol and ethanol at Ru(iii)-based electrodes resulted in activity as high as 47.2%, although the activity of the material decayed with time. The interplay of the dopant metal and copper(ii), and the long-term performance are also discussed.

Recent advances in the nanoengineering of electrocatalysts for CO2 reduction.

Emissions of CO2 from fossil fuel combustion and industrial processes have been regarded as the dominant cause of global warming. Electrochemical CO2 reduction (ECR), ideally in aqueous media, could potentially solve this problem by the storage of energy from renewable sources in the form of chemical energy in fuels or value-added chemicals in a sustainable manner. However, because of the sluggish reaction kinetics of the ECR, efficient, selective, and durable electrocatalysts are required to increase the rate this reaction. Despite considerable progress in using bulk metallic electrodes for catalyzing the ECR, greater efforts are still needed to tackle this grand challenge. In this Review, we highlight recent progress in using nanoengineering strategies to promote the electrocatalysts for the ECR. Through these approaches, considerable improvements in catalytic performance have been achieved. An outlook of future developments in applying and optimizing these strategies is also proposed.

Heteroatom-doped carbon materials and their composites as electrocatalysts for CO2 reduction

We review heteroatom-doped carbon materials and composites as electrocatalysts for CO2 electrochemical reduction to various high-value fuels and chemicals.

Hollow CuS Microcube Electrocatalysts for CO2 Reduction Reaction

AbstractElectrocatalytic carbon dioxide reduction reaction (CO2RR) is a promising strategy to mitigate or to address the issues caused by increasing CO2 emissions, but the implementation of such a technique highly depends on the exploration of highly efficient electrocatalysts toward the CO2RR. Here, we report a reliable route for the synthesis of hollow CuS microcubes (h‐CuS MCs) through a galvanic replacement reaction of the Cu2O microcube (Cu2O MC) precursor. A variety of characteristic techniques, including X‐ray diffraction, X‐ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy, were performed to study the morphology, crystalline structure, and surface properties. Systematic electrochemical studies demonstrate that the electrocatalytic activity for CO2RR is sensitive to crystalline structure, morphology, and size of Cu‐based materials. The h‐CuS MCs manifest the highest electrocatalytic activity upon electrocatalyzing CO2RR among the set of Cu‐based materials tested, as evidenced by a rather low overpotential and an enhanced faradaic efficiency for CO production.

Frontispiece: High‐Throughput Synthesis of Mixed‐Metal Electrocatalysts for CO2 Reduction

Frontispiece: High‐Throughput Synthesis of Mixed‐Metal Electrocatalysts for CO₂ Reduction

Frontispiz: High‐Throughput Synthesis of Mixed‐Metal Electrocatalysts for CO2 Reduction

Frontispiz: High‐Throughput Synthesis of Mixed‐Metal Electrocatalysts for CO₂ Reduction

Solvothermally-Prepared Cu2 O Electrocatalysts for CO2 Reduction with Tunable Selectivity by the Introduction of p-Block Elements.

The electroreduction of CO2 to fuels and chemicals is an attractive strategy for the valorization of CO2 emissions. In this study, a Cu2 O electrocatalyst prepared by a simple and potentially scalable solvothermal route effectively targeted CO evolution at low-to-moderate overpotentials [with a current efficiency for CO (CECO ) of ca. 60 % after 12 h at -0.6 V vs. reversible hydrogen electrode, RHE], and its selectivity was tuned by the introduction of p-block elements (In, Sn, Ga, Al) into the catalyst. SEM, HRTEM, and voltammetric analyses revealed that the Cu2 O catalyst undergoes extensive surface restructuring (favorable for CO evolution) under the reaction conditions. The modification of Cu2 O with Sn and In further enhanced the current efficiency (CE) for CO (ca. 75 % after 12 h at -0.6 V). In contrast, the introduction of Al altered the selectivity profile of the catalyst significantly, decreasing the selectivity toward CO but promoting the reduction of CO2 to ethylene (CE≈7 %), n-propanol, and ethanol (CE≈2 % each) at -0.8 V vs. RHE. This result is related to a decreased reducibility of Al-doped Cu2 O that might preserve Cu+ species (favorable for C2 H4 production) under the reaction conditions, which is supported by XRD, X-ray photoelectron spectroscopy, and H2 temperature-programmed reduction observations.

High-Throughput Synthesis of Mixed-Metal Electrocatalysts for CO2 Reduction.

The utilization of CO2 as a feedstock requires fundamental breakthroughs in catalyst design. The efficiencies and activities of pure metal electrodes towards the CO2 reduction reaction are established, but the corresponding data on mixed-metal systems are not as well developed. In this study we show that the near-infrared driven decomposition (NIRDD) of solution-deposited films of metal salts and subsequent electrochemical reduction offers the unique opportunity to form an array of mixed-metal electrocatalyst coatings with excellent control of the metal stoichiometries. This synthetic method enabled us to develop an empirical structure-property correlation to help inform the development of optimized CO2 catalyst compositions.

High‐Throughput Synthesis of Mixed‐Metal Electrocatalysts for CO2 Reduction

AbstractThe utilization of CO2 as a feedstock requires fundamental breakthroughs in catalyst design. The efficiencies and activities of pure metal electrodes towards the CO2 reduction reaction are established, but the corresponding data on mixed‐metal systems are not as well developed. In this study we show that the near‐infrared driven decomposition (NIRDD) of solution‐deposited films of metal salts and subsequent electrochemical reduction offers the unique opportunity to form an array of mixed‐metal electrocatalyst coatings with excellent control of the metal stoichiometries. This synthetic method enabled us to develop an empirical structure–property correlation to help inform the development of optimized CO2 catalyst compositions.

Investigation of Electrocatalysts for Selective Reduction of CO2 to CO: Monitoring the Reaction Products by on line Mass Spectrometry and Gas Chromatography

The carbon dioxide electrocatalytic reduction is central for the development of regenerative cycles of electrochemical energy conversion and storage. Herein, the gaseous products of the CO2 electroreduction were monitored by using an electrochemical cell on line coupled to a differential electrochemical mass spectrometer (DEMS), aiming at searching for electrocatalysts with high selectivity for CO formation. The results showed that, among the studied materials, the Cu4Sn/C alloy nanoparticles were stable during potentiostatic polarizations as revealed by in situ X-ray absorption spectroscopy (XAS), and the on line DEMS measurements showed the production of CO, suppression of methane and ethylene formations, and diminishing of the hydrogen evolution reaction, in relation to that on pure Cu2O-Cu/C. The faradaic efficiencies for CO formation were 13 and 23% for Cu4Sn/C and Au/C (a known electrocatalyst for CO), respectively, determined by experiments of in line gas chromatography (GC). The selectivity of Cu4Sn/C for CO formation was ascribed to the role of Sn atoms on stabilizing adsorbed HCOO intermediates, and hindering further hydrogenation, letting CO free for desorption. These results are expected to be used as a guide for further development of electrocatalysts with a fine-tuning of composition for increasing the faradaic efficiency of CO2 electroreduction to CO.

Hierarchical Mesoporous SnO2 Nanosheets on Carbon Cloth: A Robust and Flexible Electrocatalyst for CO2 Reduction with High Efficiency and Selectivity.

Electrochemical reduction of CO2 into liquid fuels is a promising approach to achieve a carbon-neutral energy cycle. However, conventional electrocatalysts usually suffer from low energy efficiency and poor selectivity and stability. A 3D hierarchical structure composed of mesoporous SnO2 nanosheets on carbon cloth is proposed to efficiently and selectively electroreduce CO2 to formate in aqueous media. The electrode is fabricated by a facile combination of hydrothermal reaction and calcination. It exhibits an unprecedented partial current density of about 45 mA cm-2 at a moderate overpotential (0.88 V) with high faradaic efficiency (87±2 %), which is even larger than most gas diffusion electrodes. Additionally, the electrode also demonstrates flexibility and long-term stability. The superior performance is attributed to the robust and highly porous hierarchical structure, which provides a large surface area and facilitates charge and mass transfer.

Hierarchical Mesoporous SnO2 Nanosheets on Carbon Cloth: A Robust and Flexible Electrocatalyst for CO2 Reduction with High Efficiency and Selectivity

AbstractElectrochemical reduction of CO2 into liquid fuels is a promising approach to achieve a carbon‐neutral energy cycle. However, conventional electrocatalysts usually suffer from low energy efficiency and poor selectivity and stability. A 3D hierarchical structure composed of mesoporous SnO2 nanosheets on carbon cloth is proposed to efficiently and selectively electroreduce CO2 to formate in aqueous media. The electrode is fabricated by a facile combination of hydrothermal reaction and calcination. It exhibits an unprecedented partial current density of about 45 mA cm−2 at a moderate overpotential (0.88 V) with high faradaic efficiency (87±2 %), which is even larger than most gas diffusion electrodes. Additionally, the electrode also demonstrates flexibility and long‐term stability. The superior performance is attributed to the robust and highly porous hierarchical structure, which provides a large surface area and facilitates charge and mass transfer.

Controlled electropolymerisation of a carbazole-functionalised iron porphyrin electrocatalyst for CO2 reduction.

Using a one-step electropolymerisation procedure, CO2 absorbing microporous carbazole-functionalised films of iron porphyrins are prepared in a controlled manner. The electrocatalytic reduction of CO2 for these films is investigated to elucidate their efficiency and the origin of their ultimate degradation.

A DFT-based genetic algorithm search for AuCu nanoalloy electrocatalysts for CO₂ reduction.

Using a DFT-based genetic algorithm (GA) approach, we have determined the most stable structure and stoichiometry of a 309-atom icosahedral AuCu nanoalloy, for potential use as an electrocatalyst for CO2 reduction. The identified core-shell nano-particle consists of a copper core interspersed with gold atoms having only copper neighbors and a gold surface with a few copper atoms in the terraces. We also present an adsorbate-dependent correction scheme, which enables an accurate determination of adsorption energies using a computationally fast, localized LCAO-basis set. These show that it is possible to use the LCAO mode to obtain a realistic estimate of the molecular chemisorption energy for systems where the computation in normal grid mode is not computationally feasible. These corrections are employed when calculating adsorption energies on the Cu, Au and most stable mixed particles. This shows that the mixed Cu135@Au174 core-shell nanoalloy has a similar adsorption energy, for the most favorable site, as a pure gold nano-particle. Cu, however, has the effect of stabilizing the icosahedral structure because Au particles are easily distorted when adding adsorbates.

ChemInform Abstract: Molybdenum Sulfides and Selenides as Possible Electrocatalysts for CO2 Reduction

AbstractDFT calculations

Molybdenum Sulfides and Selenides as Possible Electrocatalysts for CO2 Reduction

AbstractLinear scaling relations between reaction intermediates pose a fundamental limitation to the CO2 reduction activity of transition‐metal catalysts. To design improved catalysts, we propose to break these scaling relations by binding key reaction intermediates to different sites. Using density functional theory, we demonstrate this principle in the active edge sites in MoS2, MoSe2, and Ni‐doped MoS2. These edges show the unique property of selectively binding COOH and CHO to bridging S or Se atoms and CO to the metal atom. DFT calculations suggest a significant improvement in CO2 reduction activity over the transition metals. Our results point to the broader application of the active edge sites of transition‐metal dichalcogenides in complex electrochemical processes.

Inside Back Cover: Molybdenum Sulfides and Selenides as Possible Electrocatalysts for CO2Reduction (ChemCatChem 7/2014)

The electrochemical reduction of CO2 The cover picture shows MoS2 and Ni-doped MoS2 catalysts, and the reaction path of CO2 electrochemical reduction to CH4 on Ni-doped MoS2. In their Full Paper on p. 1899 ff., J. K. Nørskov and co-workers describe how their density functional theory calculations predict MoS2, MoSe2, and Ni-doped MoS2 to have significantly improved activity for CO2 electrochemical reduction over the best transition metal catalysts. This activity arises from the binding of intermediates to different sites, which allows for deviations from the scaling relations between the intermediates on transition metals. Their results point to the broader application of the active edge sites of transition metal dichalcogenides in complex electrochemical processes.