We report a joint experimental−computational mechanistic study of electrochemical reduction of CO 2 to CH 4 , catalyzed by solid-state Fe−N−C catalysts, which feature atomically dispersed, catalytically active Fe−N x sites and represent one of the very rare examples of solid, non-Cu-based electrocatalysts that yield hydrocarbon products. Work reported here focuses on the identification of plausible mechanistic pathways from CO 2 to various C 1 products including methane. It is found that Fe−N x sites convert only CO 2 , CO, and CH 2 O into methane, whereas CH 3 OH appears to be an end product. Distinctly different pH dependence of the catalytic CH 4 evolution from CH 2 O in comparison with that of CO 2 and CO reduction indicates differences in the proton participation of ratedetermining steps. By comparing the experimental observations with density functional theory derived free energy diagrams of reactive intermediates along the CO 2 reduction reaction coordinates, we unravel the dominant mechanistic pathways and roles of CO and CH 2 O during the catalytic CO 2 -to-CH 4 cascades and their rate-determining steps. We close with a comprehensive reaction network of CO 2 RR on single-site Fe−N−C catalysts, which may prove useful in developing efficient, non-Cubased catalysts for hydrocarbon production.

Carbon materials doped with nitrogen are active catalysts for the electrochemical two-electron oxygen reduction reaction (ORR) to hydrogen peroxide. Insights into the individual role of the various chemical nitrogen functionalities in the H O production, however, have remained scarce. Here, we explore a catalytically very active family of nitrogen-doped porous carbon materials, prepared by direct pyrolysis of ordered mesoporous carbon (CMK-3) with polyethylenimine (PEI). Voltammetric rotating ring-disk analysis in combination with chronoamperometric bulk electrolysis measurements in electrolysis cells demonstrate a pronounced effect of the applied potentials, current densities, and electrolyte pH on the H O selectivity and absolute production rates. H O selectivity up to 95.3 % was achieved in acidic environment, whereas the largest H O production rate of 570.1 mmol g h was observed in neutral solution. X-ray photoemission spectroscopy (XPS) analysis suggests a key mechanistic role of pyridinic-N in the catalytic process in acid, whereas graphitic-N groups appear to be catalytically active moieties in neutral and alkaline conditions. Our results contribute to the understanding and aid the rational design of efficient carbon-based H O production catalysts.

Metal−nitrogen−carbon (MNC) catalysts represent a potential means of reducing cathode catalyst costs in low temperature fuel cell cathodes. Knowledge-based improvements have been hampered by the difficulty to deconvolute active site density and intrinsic turnover frequency. In the present work, MNC catalysts with a variety of secondary nitrogen precursors are addressed. CO chemisorption in combination with Mossbauer spectroscopy are utilized in order to unravel previously inaccessible relations between active site density, turnover frequency, and active site utilization. This analysis provides a more fundamental description and understanding of the origin of the catalytic reactivity; it also provides guidelines for further improvements. Secondary nitrogen precursors impact quantity, quality, dispersion, and utilization of active sites in distinct ways. Secondary nitrogen precursors with high nitrogen content and micropore etching capabilities are most effective in improving catalysts performance.

Employing solid ceramic electrolyte in sodium (Na) metal batteries enables safe and cost-effective energy storage solution toward the advent of sustainable energy. Nevertheless, the development of solid-state Na batteries is hindered by the large interfacial charge transfer resistance between electrodes and solid electrolyte. Here, a novel and scalable design approach is utilized to significantly reduce the interfacial resistance through the direct growth of graphene-like interlayer on Na+ superionic conductor (NASICON) ceramic electrolyte, resulting in a 10-fold decrease of interfacial resistance. Benefiting from the graphene regulated NASICON, extremely stable Na plating/stripping cycling performance using solid electrolyte at a current density up to 1 mA/cm2 with a cycling capacity of 1 mAh/cm2 for 500 cycles (1000 h) is demonstrated for the first time. The surface of Na electrode after 1000 h of cycling remained smooth because of uniform Na+ flux across graphene-coated-NASICON/Na interface enabled by the abundant graphene defects network for efficient Na+ transport. Solid-state room temperature battery consists of graphene-regulated NASICON electrolyte, Na3V2(PO4)3 cathode and Na anode delivered a reversible initial capacity of 108 mAh/g at 1C current density for 300 cycles with 85% capacity retention, far superior than the battery with pristine NASICON. This work can be a valuable contribution toward a safe and stable solid-state Na metal battery system, and provide insights for solid-state lithium metal batteries as well.

By means of transient UV-visible absorption spectra/fluorescence spectra, combined with electronic structure calculations, the present work focuses on characterizing the photophysical and electronic properties of five PCBM-like C(60) derivatives (F1, F2, F3, F4, and F5) and understanding how these properties are expected to affect the photovoltaic performance of polymer solar cells (PSCs) with those molecules as acceptors. Spectral data reveal that the fluorescence quantum yields (Φ(F)) are enhanced and the triplet quantum yields (Φ(T)) are lowered for the five PCBM-like C(60) derivatives as compared to those of the pristine C(60), suggesting that functionalization of a C═C double bond perturbs the fullerene's π-system and breaks the I(h) symmetry of pristine C(60), which results in modifications of photophysical properties of the fullerene derivatives. PBEPBE/6-311G(d,p)//PBEPBE/6-31G(d) level of electronic structure calculations yields the HOMO-LUMO gaps and LUMO energies, showing that the electron-withdrawing effect induced by the side chain functional groups perturbs LUMO energies, from which different open circuit voltages V(oc) are resulted. The predicted V(oc) from our calculation agrees with previous experiment results. Basically, we found that functionalization of a C═C double bond sustains the fullerene structure and its electron affinitive properties. Adducted side chains contribute to adjust the HOMO-LUMO gap and LUMO levels of the acceptors to improve open circuit voltage. The results could provide fundamental insights for understanding how structural modifications influence the photovoltaic performance, which paves a way for guiding the synthesis of new fullerene derivatives with improved performance in polymer solar cells.