Direct electrochemical reduction of CO2 to fuels and chemicals using renewable electricity has attracted significant attention partly due to the fundamental challenges related to reactivity and selectivity, and partly due to its importance for industrial CO2-consuming gas diffusion cathodes. Here, we present advances in the understanding of trends in the CO2 to CO electrocatalysis of metal- and nitrogen-doped porous carbons containing catalytically active M–Nx moieties (M = Mn, Fe, Co, Ni, Cu). We investigate their intrinsic catalytic reactivity, CO turnover frequencies, CO faradaic efficiencies and demonstrate that Fe–N–C and especially Ni–N–C catalysts rival Au- and Ag-based catalysts. We model the catalytically active M–Nx moieties using density functional theory and correlate the theoretical binding energies with the experiments to give reactivity-selectivity descriptors. This gives an atomic-scale mechanistic understanding of potential-dependent CO and hydrocarbon selectivity from the M–Nx moieties and it provides predictive guidelines for the rational design of selective carbon-based CO2 reduction catalysts.

In this work, we propose four non‐coupled binding energies of intermediates as descriptors, or “genes”, for predicting the product distribution in CO2 electroreduction. Simple reactions can be understood by the Sabatier principle (catalytic activity vs. one descriptor), while more complex reactions tend to give multiple very different products and consequently the product selectivity is a more complex property to understand. We approach this, as a logistical classification problem, by grouping metals according to their major experimental product from CO2 electroreduction: H2, CO, formic acid and beyond CO* (hydrocarbons or alcohols). We compare the groups in terms of multiple binding energies of intermediates calculated by density functional theory. Here, we find three descriptors to explain the grouping: the adsorption energies of H*, COOH*, and CO*. To further classify products beyond CO*, we carry out formaldehyde experiments on Cu, Ag, and Au and combine these results with the literature to group and differentiate alcohol or hydrocarbon products. We find that the oxygen binding (adsorption energy of CH3O*) is an additional descriptor to explain the alcohol formation in reduction processes. Finally, the adsorption energy of the four intermediates, H*, COOH*, CO*, and CH3O*, can be used to differentiate, group, and explain products in electrochemical reduction processes involving CO2, CO, and carbon–oxygen compounds.

Nitrogen-doped carbon materials featuring atomically dispersed metal cations (M−N−C) are an emerging family of materials with potential applications for electrocatalysis. The electrocatalytic activity of M−N−C materials toward four-electron oxygen reduction reaction (ORR) to H 2 O is a mainstream line of research for replacing platinumgroup-metal-based catalysts at the cathode of fuel cells. However, fundamental and practical aspects of their electrocatalytic activity toward two-electron ORR to H 2 O 2 , a future green "dream" process for chemical industry, remain poorly understood. Here we combined computational and experimental efforts to uncover the trends in electrochemical H 2 O 2 production over a series of M−N−C materials (M = Mn, Fe, Co, Ni, and Cu) exclusively comprising atomically dispersed M−N x sites from molecular first-principles to bench-scale electrolyzers operating at industrial current density. We investigated the effect of the nature of a 3d metal within a series of M−N−C catalysts on the electrocatalytic activity/selectivity for ORR (H 2 O 2 and H 2 O products) and H 2 O 2 reduction reaction (H 2 O 2 RR). Co−N−C catalyst was uncovered with outstanding H 2 O 2 productivity considering its high ORR activity, highest H 2 O 2 selectivity, and lowest H 2 O 2 RR activity. The activity−selectivity trend over M−N−C materials was further analyzed by density functional theory, providing molecular-scale understandings of experimental volcano trends for four-and two-electron ORR. The predicted binding energy of HO* intermediate over Co−N−C catalyst is located near the top of the volcano accounting for favorable two-electron ORR. The industrial H 2 O 2 productivity over Co−N−C catalyst was demonstrated in a microflow cell, exhibiting an unprecedented production rate of more than 4 mol peroxide g catalyst −1 h −1 at a current density of 50 mA cm −2 .

This study explores the kinetics, mechanism, and active sites of the CO2 electroreduction reaction (CO2RR) to syngas and hydrocarbons on a class of functionalized solid carbon-based catalysts. Commercial carbon blacks were functionalized with nitrogen and Fe and/or Mn ions using pyrolysis and acid leaching. The resulting solid powder catalysts were found to be active and highly CO selective electrocatalysts in the electroreduction of CO2 to CO/H2 mixtures outperforming a low-area polycrystalline gold benchmark. Unspecific with respect to the nature of the metal, CO production is believed to occur on nitrogen functionalities in competition with hydrogen evolution. Evidence is provided that sufficiently strong interaction between CO and the metal enables the protonation of CO and the formation of hydrocarbons. Our results highlight a promising new class of low-cost, abundant electrocatalysts for synthetic fuel production from CO2 .

We demonstrate the direct electrochemical conversion of CO2 to CO using solid state Ni–N–C carbon catalysts characterized by a coordinative molecular Ni–Nx active moiety at industrial current densities of up to 700 mA cm−2 with faradaic efficiencies superior to those of the state-of-the-art AgOx electrocatalysts.