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1. Directing the reactivity of metal hydrides for selective CO 2 reduction

   https://doi.org/10.1073/pnas.1811396115  

   Ceballos, Bianca M. ; Yang, Jenny Y. ( November 2018 , Proceedings of the National Academy of Sciences)

   A critical challenge in electrocatalytic CO₂reduction to renewable fuels is product selectivity. Desirable products of CO₂reduction require proton equivalents, but key catalytic intermediates can also be competent for direct proton reduction to H₂. Understanding how to manage divergent reaction pathways at these shared intermediates is essential to achieving high selectivity. Both proton reduction to hydrogen and CO₂reduction to formate generally proceed through a metal hydride intermediate. We apply thermodynamic relationships that describe the reactivity of metal hydrides with H⁺and CO₂to generate a thermodynamic product diagram, which outlines the free energy of product formation as a function of proton activity and hydricity (∆G_H−), or hydride donor strength. The diagram outlines a region of metal hydricity and proton activity in which CO₂reduction is favorable and H⁺reduction is suppressed. We apply our diagram to inform our selection of [Pt(dmpe)₂](PF₆)₂as a potential catalyst, because the corresponding hydride [HPt(dmpe)₂]⁺has the correct hydricity to access the region where selective CO₂reduction is possible. We validate our choice experimentally; [Pt(dmpe)₂](PF₆)₂is a highly selective electrocatalyst for CO₂reduction to formate (>90% Faradaic efficiency) at an overpotential of less than 100 mV in acetonitrile with no evidence of catalyst degradation after electrolysis. Our report of a selective catalyst for CO₂reduction illustrates how our thermodynamic diagrams can guide selective and efficient catalyst discovery.

    

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2. Cobalt telluride electrocatalyst for selective electroreduction of CO2 to value-added chemicals

   https://doi.org/10.1007/s40243-022-00211-6  

   Saxena, Apurv ; Singh, Harish ; Nath, Manashi ( July 2022 , Materials for Renewable and Sustainable Energy)

   Recent emphasis on carbon dioxide utilization has necessitated the exploration of different catalyst compositions other than copper-based systems that can significantly improve the activity and selectivity towards specific CO₂ reduction products at low applied potential. In this study, a binary CoTe has been reported as an efficient electrocatalyst for CO₂reduction in aqueous medium under ambient conditions at neutral pH. CoTe showed high Faradaic efficiency and selectivity of 86.83 and 75%, respectively, for acetic acid at very low potential of − 0.25 V vs RHE. More intriguingly, C1 products like formic acid was formed preferentially at slightly higher applied potential achieving high formation rate of 547.24 μmol cm⁻² h⁻¹ at − 1.1 V vs RHE. CoTe showed better CO2RR activity when compared with Co₃O₄, which can be attributed to the enhanced electrochemical activity of the catalytically active transition metal center as well as improved intermediate adsorption on the catalyst surface. While reduced anion electronegativity and improved lattice covalency in tellurides enhance the electrochemical activity of Co, high d-electron density improves the intermediate CO adsorption on the catalyst site leading to CO₂reduction at lower applied potential and high selectivity for C₂products. CoTe also shows stable CO2RR catalytic activity for 50 h and low Tafel slope (50.3 mV dec^–1) indicating faster reaction kinetics and robust functionality. Selective formation of value-added C₂products with low energy expense can make these catalysts potentially viable for integration with other CO₂capture technologies thereby, helping to close the carbon loop.

    

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3. Solving the structure of “single-atom” catalysts using machine learning – assisted XANES analysis

   https://doi.org/10.1039/D1CP05513E  

   Xiang, Shuting ; Huang, Peipei ; Li, Junying ; Liu, Yang ; Marcella, Nicholas ; Routh, Prahlad K. ; Li, Gonghu ; Frenkel, Anatoly I. ( February 2022 , Physical Chemistry Chemical Physics)

   “Single-atom” catalysts (SACs) have demonstrated excellent activity and selectivity in challenging chemical transformations such as photocatalytic CO 2 reduction. For heterogeneous photocatalytic SAC systems, it is essential to obtain sufficient information of their structure at the atomic level in order to understand reaction mechanisms. In this work, a SAC was prepared by grafting a molecular cobalt catalyst on a light-absorbing carbon nitride surface. Due to the sensitivity of the X-ray absorption near edge structure (XANES) spectra to subtle variances in the Co SAC structure in reaction conditions, different machine learning (ML) methods, including principal component analysis, K-means clustering, and neural network (NN), were utilized for in situ Co XANES data analysis. As a result, we obtained quantitative structural information of the SAC nearest atomic environment, thereby extending the NN-XANES approach previously demonstrated for nanoparticles and size-selective clusters. 

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4. Advances in Electrochemical Modification Strategies of 5‐Hydroxymethylfurfural

   https://doi.org/10.1002/cssc.202100139  

   Simoska, Olja ; Rhodes, Zayn ; Weliwatte, Samali ; Cabrera‐Pardo, Jaime R. ; Gaffney, Erin M. ; Lim, Koun ; Minteer, Shelley D. ( February 2021 , ChemSusChem)

   The development of electrochemical catalytic conversion of 5‐hydroxymethylfurfural (HMF) has recently gained attention as a potentially scalable approach for both oxidation and reduction processes yielding value‐added products. While the possibility of electrocatalytic HMF transformations has been demonstrated, this growing research area is in its initial stages. Additionally, its practical applications remain limited due to low catalytic activity and product selectivity. Understanding the catalytic processes and design of electrocatalysts are important in achieving a selective and complete conversion into the desired highly valuable products. In this Minireview, an overview of the most recent status, advances, and challenges of oxidation and reduction processes of HMF was provided. Discussion and summary of voltammetric studies and important reaction factors (e. g., catalyst type, electrode material) were included. Finally, biocatalysts (e. g., enzymes, whole cells) were introduced for HMF modification, and future opportunities to combine biocatalysts with electrochemical methods for the production of high‐value chemicals from HMF were discussed.

    

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5. Electro‐ and Photochemical Reduction of CO 2 by Molecular Manganese Catalysts: Exploring the Positional Effect of Second‐Sphere Hydrogen‐Bond Donors

   https://doi.org/10.1002/cssc.202001940  

   Roy, Sayontani Sinha ; Talukdar, Kallol ; Jurss, Jonah W. ( November 2020 , ChemSusChem)

   A series of molecular Mn catalysts featuring aniline groups in the second‐coordination sphere has been developed for electrochemical and photochemical CO₂reduction. The arylamine moieties were installed at the 6 position of 2,2’‐bipyridine (bpy) to generate a family of isomers in which the primary amine is located at theortho‐(1‐Mn),meta‐(2‐Mn), orpara‐site (3‐Mn) of the aniline ring. The proximity of the second‐sphere functionality to the active site is a critical factor in determining catalytic performance. Catalyst1‐Mn, possessing the shortest distance between the amine and the active site, significantly outperformed the rest of the series and exhibited a 9‐fold improvement in turnover frequency relative to parent catalyst Mn(bpy)(CO)₃Br (901 vs. 102 s⁻¹, respectively) at 150 mV lower overpotential. The electrocatalysts operated with high faradaic efficiencies (≥70 %) for CO evolution using trifluoroethanol as a proton source. Notably, under photocatalytic conditions, a concentration‐dependent shift in product selectivity from CO (at high [catalyst]) to HCO₂H (at low [catalyst]) was observed with turnover numbers up to 4760 for formic acid and high selectivities for reduced carbon products.

    

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