CoxNi1−x nanoalloys on N-doped carbon nanofibers: Electronic regulation toward efficient electrochemical CO2 reduction

A Multiscale Strategy to Construct Cobalt Nanoparticles Confined within Hierarchical Carbon Nanofibers for Efficient CO2 Electroreduction

The efficiency of CO₂ electroreduction has been largely limited by the activity of the catalysts as well as the three-phase interface. Herein, a multiscale strategy is proposed to synthesize hierarchical nanofibers covered by carbon nanotubes and embedded with cobalt nanoparticles (Co/CNT/HCNF). The confinement effect of carbon nanotubes can restrict the diameter of the cobalt particles down to several nanometers and prevent the easy corrosion of these nanoparticles. The three-dimensional carbon nanofibers, in size range of several hundred nanometers, improve the electrochemically active surface area, facilitate electron transfer, and accelerate CO₂ transportation. These cross-linked carbon nanofibers eventually form a freestanding Co/CNT/HCNF membrane of dozens of square centimeters. Consequently, Co/CNT/HCNF produces CO with 97% faradaic efficiency at only -0.4 V_RHE cathode potential in an H-type cell. From the regulation of catalyst nanostructure to the design of macrography devices, Co/CNT/HCNF membrane can be directly used as the gas-diffusion compartment in a flow cell device. Co/CNT/HCNF membrane generates CO with faradaic efficiencies higher than 90% and partial current densities greater than 300 mA cm^-2 for at least 100-h stability. This strategy provides a successful example of efficient catalysts for CO₂ electroreduction and also has the feasibility in other self-standing energy conversion devices.

Theoretical Insights on Au-based Bimetallic Alloy Electrocatalysts for Nitrogen Reduction Reaction with High Selectivity and Activity

Electrochemical reduction of nitrogen to produce ammonia at moderate conditions in aqueous solutions holds great prospect but also faces huge challenges. Considering the high selectivity of Au-based materials to inhibit competitive hydrogen evolution reaction (HER) and high activity of transition metals such as Fe and Mo toward the nitrogen reduction reaction (NRR), it was proposed that Au-based alloy materials could act as efficient catalysts for N₂ fixation based on density functional theory simulations. Only on Mo₃ Au(111) surface the adsorption of N₂ is stronger than H atom. Thermodynamics combined with kinetics studies were performed to investigate the influence of composition and ratio of Au-based alloys on NRR and HER. The binding energy and reorganization energy affected performance for the initial N₂ activation and hydrogenation process. By considering the free-energy diagram, the computed potential-determining step was either the first or the fifth hydrogenation step on metal catalysts. The optimum catalytic activity could be achieved by adjusting atomic proportion in alloys to make all intermediate species exhibit moderate adsorption. Free-energy diagrams of N₂ hydrogenation via Langmuir-Hinshelwood mechanism and hydrogen evolution via Tafel mechanism were compared to reveal that the Mo₃ Au surface showed satisfactory catalytic performance by simultaneously promoting NRR and suppressing HER. Theoretical simulations demonstrated that Au-Mo alloy materials could be applied as high-performance electrocatalysts for NRR.

Selective CO2 reduction towards a single upgraded product: a minireview on multi-elemental copper-free electrocatalysts

Electrocatalytic conversion of the greenhouse gas carbon dioxide to liquid fuels or upgraded chemicals is a critical strategy to mitigate anthropogenic climate change. To this end, we urgently need high-performance CO₂ reduction catalysts.

Three-Dimensional Cathodes for Electrochemical Reduction of CO2: From Macro- to Nano-Engineering

Rising anthropogenic CO2 emissions and their climate warming effects have triggered a global response in research and development to reduce the emissions of this harmful greenhouse gas. The use of CO2 as a feedstock for the production of value-added fuels and chemicals is a promising pathway for development of renewable energy storage and reduction of carbon emissions. Electrochemical CO2 conversion offers a promising route for value-added products. Considerable challenges still remain, limiting this technology for industrial deployment. This work reviews the latest developments in experimental and modeling studies of three-dimensional cathodes towards high-performance electrochemical reduction of CO2. The fabrication-microstructure-performance relationships of electrodes are examined from the macro- to nanoscale. Furthermore, future challenges, perspectives and recommendations for high-performance cathodes are also presented.