Single Ni atoms with higher positive charges induced by hydroxyls for electrocatalytic CO2 reduction

Customizing pyridinic nitrogen coordination in Ni-N-C for electrocatalytic CO2reduction towards CO

Nickel anchored N-doped carbon electrocatalysts (Ni-N-C) are rapidly developed for the electrochemical reduction reaction of carbon dioxide (CO2RR). However, the high-performanced Ni-N-C analogues design for CO2RR remains bewilderment, for the reason lacking of definite guidance for its structure-activity relationship. Herein, the correlation between the proportion of nitrogen species derived from various nitrogen sources and the CO2RR activity of Ni-N-C is investigated. The x-ray photoelectron spectroscopy (XPS) spectrum combined with the CO2RR performance results show that pyridinic-N content has a positive correlation with CO2RR activity. Moreover, density functional theory (DFT) demonstrates that pyridinic-N coordinated Ni-N4sites offers optimized free energy and favorable selectivity towards CO2RR compared with pyrrolic-N. Accordingly, Ni-Na-C with highest pyridinic-N content (ammonia as nitrogen source) performs superior CO2RR activity, with the maximum carbon monoxide faradaic efficiency (FECO) of 99.8% at -0.88 V vs. RHE and the FECOsurpassing 95% within potential ranging of -0.88 to -1.38 V vs. RHE. The building of this parameter for CO2RR activity of Ni-N-C give instructive forecast for low-cost and highly active CO2RR electrocatalysts.

Template-Sacrificing Synthesis of Well-Defined Asymmetrically Coordinated Single-Atom Catalysts for Highly Efficient CO2 Electrocatalytic Reduction

Although various single-atom catalysts have been designed, atomically engineering their coordination environment remains a great challenge. Herein, a one-pot template-sacrificing pyrolysis approach is developed to synthesize well-defined Ni-N₄-O catalytic sites on highly porous graphitic carbon for electrocatalytic CO₂ reduction to CO with high Faradaic efficiency (maximum of 97.2%) in a wide potential window (-0.56 to -1.06 V vs RHE) and with high stability. In-depth experimental and theoretical studies reveal that the axial Ni-O coordination introduces asymmetry to the catalytic center, leading to lower Gibbs free energy for the rate-limiting step, strengthened binding with *COOH, and a weaker association with *CO. The present results demonstrate the successful atomic-level coordination environment engineering of high-surface-area porous graphitic carbon-supported Ni single-atom catalysts (SACs), and the demonstrated method can be applied to synthesize an array of SACs (metal-N₄-O) for various catalysis applications.

Designing electrode materials for the electrochemical reduction of carbon dioxide

Electrochemical reduction of carbon dioxide is a viable alternative for reducing fossil fuel consumption and reducing atmospheric CO₂ levels. Although, a wide variety of materials have been studied for electrochemical reduction of CO₂, the selective and efficient reduction of CO₂ is still not accomplished. Complex reaction mechanisms and the competing hydrogen evolution reaction further complicates the efficiency of materials. An extensive understanding of reaction mechanism is hence essential in designing an ideal electrocatalyst material. Therefore, in this review article we discuss the materials explored in the last decade with focus on their catalytic mechanism and methods to enhance their catalytic activity.

Electrochemical properties of La0.5Sr0.5Fe0.95Mo0.05O3−δ as cathode materials for IT-SOEC

Solid oxide electrolysis cells (SOECs) are a new type of high-efficiency energy conversion device that can electrolyze CO₂ efficiently and convert electricity into chemical energy. However, the lack of efficient and stable cathodes hinders the practical application of CO₂ electrolysis in SOECs. Herein, a novel perovskite oxide La_0.5Sr_0.5Fe_0.95Mo_0.05O_3−δ (LSFMo) is synthesized and used as a cathode for SOECs. The introduction of Mo significantly improves the CO₂ tolerance of the material in a reducing atmosphere and solves the problem of SrCO₃ generation in the La_0.5Sr_0.5FeO_3−δ material. Mo ion doping promotes the conductivity in a reducing atmosphere and increases the oxygen deficiencies of the material, which lowers the ohmic resistance (R_s) of the material and significantly improves the CO₂ adsorption and dissociation in the middle-frequency of polarization resistance (R_p). For example, R_p decreases from 0.49 to 0.24 Ω cm² at 800 °C under 1.2 V. Further, the reduction of R_s and R_p increases the performance improvement, and the current density is increased from 1.56 to 2.13 A cm⁻² at 800 °C under 2 V. Furthermore, LSFMo shows reasonable short-term stability during the 60 h stability test.

Mo doping solves the SrCO₃ generation of LSF as SOEC cathode and increases the oxygen deficiencies of the material, which make LSFMo possess higher electrolytic performance.

A comparative study of the effects of different TiO2 supports toward CO2 electrochemical reduction on CuO/TiO2 electrode

CuO-based electrodes possess vast potential in the field of CO₂ electrochemical reduction. Meantime, TiO₂ supports show the advantages of being non-toxic, low-cost and having high chemical stability, which render it an ideal electrocatalytic support with CuO. However, different morphologies and structures of TiO₂ supports can be obtained through various methods, leading to the discrepant electrocatalytic properties of CuO/TiO₂. In this paper, three supports, named dense TiO₂, TiO₂ nanotube and TiO₂ nanofiber, were applied to synthesize CuO/TiO₂ electrodes by thermal decomposition, and the performances of the electrocatalysts were studied. Results show that the main product of the three electrocatalysts was ethanol, but the electrochemical efficiency and reaction characteristics are obviously different. The liquid product of CuO/Dense TiO₂ is pure ethanol, however, the current efficiency is rather low owing to the higher resistance of the TiO₂ film. CuO/TiO₂ nanotube shows high conductivity and ethanol can be synthesized at low overpotential with high current efficiency, but the gas products cannot be restricted. CuO/TiO₂ nanofiber has a larger specific surface area and more active sites, which is beneficial for CO₂ reduction, and the hydrogen evolution reaction can be evidently restricted. The yield of ethanol reaches up to 6.4 μmol cm⁻² at −1.1 V (vs. SCE) after 5 h.

Electrocatalytic reduction of CO₂ on three different morphologies of CuO/TiO₂.

Homogeneous and heterogeneous molecular catalysts for electrochemical reduction of carbon dioxide

Carbon dioxide (CO2) is a greenhouse gas whose presence in the atmosphere significantly contributes to climate change. Developing sustainable, cost-effective pathways to convert CO2 into higher value chemicals is essential to curb its atmospheric presence. Electrochemical CO2 reduction to value-added chemicals using molecular catalysis currently attracts a lot of attention, since it provides an efficient and promising way to increase CO2 utilization. Introducing amino groups as substituents to molecular catalysts is a promising approach towards improving capture and reduction of CO2. This review explores recently developed state-of-the-art molecular catalysts with a focus on heterogeneous and homogeneous amine molecular catalysts for electroreduction of CO2. The relationship between the structural properties of the molecular catalysts and CO2 electroreduction will be highlighted in this review. We will also discuss recent advances in the heterogeneous field by examining different immobilization techniques and their relation with molecular structure and conductive effects.