Kinetic Understanding of Catalytic Selectivity and Product Distribution of Electrochemical Carbon Dioxide Reduction Reaction.

CO2 can be electrochemically reduced to different products depending on the nature of catalysts. In this work, we report comprehensive kinetic studies on catalytic selectivity and product distribution of the CO2 reduction reaction on various metal surfaces. The influences on reaction kinetics can be clearly analyzed from the variation of reaction driving force (binding energy difference) and reaction resistance (reorganization energy). Moreover, the CO2RR product distributions are further affected by external factors such as electrode potential and solution pH. A potential-mediated mechanism is found to determine the competing two-electron reduction products of CO2 that shifts from thermodynamics-controlled product formic acid at less negative electrode potentials to kinetic-controlled product CO at more negative electrode potentials. Based on detailed kinetic simulations, a three-parameter descriptor is applied to identify the catalytic selectivity of CO, formate, hydrocarbons/alcohols, as well as side product H2. The present kinetic study not only well explains the catalytic selectivity and product distribution of experimental results but also provides a fast way for catalyst screening.

Co-Doped Mn3 O4 Nanocubes via Galvanic Replacement Reactions for Photocatalytic Reduction of CO2 with High Turnover Number.

The synthesis of Co-doped Mn3 O4 nanocubes was achieved via galvanic replacement reactions for photo-reduction of CO2 . Co@Mn3 O4 nanocubes could efficiently photo-reduce CO2 to CO with a remarkable turnover number of 581.8 using [Ru(bpy)3 ]Cl2 ⋅ 6H2 O as photosensitizer and triethanolamine as sacrificial agent in acetonitrile and water. The galvanic replaced Co species are homogeneously distributed at the outer surface of Mn3 O4 , providing catalytic active sites during CO2 reduction reactions, which facilitate the separation and migration of photogenerated charge carriers, further benefiting the outstanding photocatalytic performance of CO2 reduction. Density functional theory calculations revealed that the decreasing of conduction band maximum in Co@Mn3 O4 was beneficial to the electron attachment from the excited sensitized molecule, which promoted photocatalytic reduction of CO2 .

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.

Revealing practical specific capacity and carbonyl utilization of multi-carbonyl compounds for organic cathode materials.

Organic carbonyl compounds are regarded as promising candidates for next-generation rechargeable batteries due to their low cost, environmentally benign nature, and high capacity. The carbonyl utilization is a key issue that limits the practical specific capacity of multi-carbonyl compounds. In this work, a combination of thermodynamic computation and electronic structure analysis is carried out to study the influence of carbonyl type and carbonyl number on the electrochemical performance of a series of multi-carbonyl compounds by using density functional theory (DFT) calculations. By comparing discharge profiles of six tetraone compounds with different carbonyl sites, it is demonstrated that pentacene-5,7,12,14-tetraone (PT) with para-dicarbonyl and pyrene-4,5,9,10-tetraone (PTO) with ortho-dicarbonyl undergo four-lithium transfer while the other four compounds with meta-dicarbonyl fragments show only two-lithium transfer during the discharge process. By further increasing the carbonyl number, the electrochemical performance of molecules with similar para-dicarbonyl sites to PT can not be strongly improved. Among all the studied multi-carbonyl compounds, triphenylene-2,3,6,7,10,11-hexaone (TPHA) and tribenzo[f,k,m]tetraphen-2,3,6,7,11,12,15,16-octaone (TTOA) with similar ortho-dicarbonyl sites to PTO exhibit the best electrochemical performance due to simultaneous high specific capacity and high discharge voltage. Our results offer evidence that conjugated multiple-carbonyl molecules with ortho-dicarbonyl sites are promising in developing high energy-density organic rechargeable batteries.