To achieve a better understanding of the CO2 reduction reaction on carbon-based electrocatalysts, we synthesized a library of nitrogen-doped carbonaceous materials with atomically dispersed 3d transition metals and corresponding metal-free electrocatalysts. The sacrificial support method was used yielding catalyst materials of high dispersity and high graphitic content. The resulting electrocatalysts were impurity free, hence allowing a better understanding of the mechanism of CO2 reduction. By combining the electrochemical results with density functional theory, we were able to separate the electrocatalysts into several categories, based on their CO2 → COOHads free energy and their COads binding strength. The “strong-CO binder” electrocatalysts (e.g., Cr, Mn and Fe–N–C) achieved a Faradaic efficiency up to 50% at −0.35 V vs. RHE (at pH = 7.5, in 0.1 M phosphate buffer). Such Faradaic efficiency was also achieved for a metal-free electrocatalyst, therefore showing the high activity of the metal-free, N-containing, moieties toward the CO2 reduction reaction. This was confirmed by near ambient pressure X-ray photoelectron spectroscopy that confirmed pyridinic and hydrogenated (pyrrolic) nitrogen moieties act as preferential adsorption sites for the CO2 on the Fe–N–C catalyst surface.

Atomically dispersed (or single atom) iron-nitrogen-carbon (Fe-N-C) catalysts are promising alternatives to platinum group metals (PGM) nanoparticles supported on dispersed carbon as a cathode material in proton exchange membrane fuel cells. Here, the degradation mechanism of Fe-N-C catalysts, synthesized by the sacrificial support method (SSM), was investigated by conducting accelerated stress tests under "load cycling" protocol (i.e. from 0.6 to 1.0 V vs. the reversible hydrogen electrode, RHE).Electrocatalyst activity towards the oxygen reduction reaction (ORR) was studied for a SSM-derived material, obtained by a single pyrolysis under 7% H 2 atmosphere (Fe-HT 1 ) and juxtaposed to that of a catalyst derived from the same sample, but subjugated to a second pyrolysis under 10% NH 3 (noted as Fe-HT 2 ). Several findings can be highlighted:(i) the second pyrolysis results in a skewing of the mesopores size toward higher diameter, along with an increase in iron content and N-pyridinic moieties, leading to a combined benefit in terms of ORR activity and selectivity; (ii) the morphological changes of these catalysts during ageing are drastically different depending on whether they were exposed

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Using molecular probes that have unique spectral signatures and have strong selective binding to the potential active sites allows elucidating the mechanism of different reactions. The mechanism of oxygen reduction reaction in metal−nitrogen−carbon (MNC) catalysts has been studied by using a bisphosphonate complexing agent, which improves the selectivity of ORR by blocking the protonated and hydrogenated nitrogen that are catalyzing the partial reduction of oxygen to hydrogen peroxide. A combination of theoretical, electrochemical and spectroscopic with focus on near-ambient pressure X-ray photoelectron spectroscopy is used to directly probe the competition between binding of oxygen and molecular probe to the surface of MNC catalyst and to identify the role of different types of nitrogen in the mechanism of ORR.