Summary The morphology of electrode materials is often overlooked when comparing different carbon-based electrocatalysts for carbon dioxide reduction. To investigate the role of morphological attributes, we studied polymer-derived, interconnected, N-doped carbon structures with uniformly sized meso or macropores, differing only in the pore size. We found that the carbon dioxide reduction selectivity (versus the hydrogen evolution reaction) increased around three times just by introducing the porosity into the carbon structure (with an optimal pore size of 27 nm). We attribute this change to alterations in the wetting and CO 2 adsorption properties of the carbon catalysts. These insights offer a new platform to advance CO 2 reduction performance by only morphological engineering of the electrocatalyst.

Of the myriad electrode materials that have been used for electrochemical (EC) and photoelectrochemical (PEC) reduction of carbon dioxide in aqueous media, copper oxide/copper interfaces have shown a remarkable range of hydrocarbon and oxygenated products including acids, aldehydes, ketones, and alcohols. This Perspective highlights experimental evidence for the fact that both EC and PEC reduction scenarios have similar chemical and morphological underpinnings in the in situ formation of copper nano-or microcubes on the (photo)cathode surface. Recent rapid developments in our fundamental understanding of these interfaces and areas requiring further studies are discussed in light of recent studies in the authors' laboratories and elsewhere. 46 range of electrode materials and electrolytes have been 47 deployed for the EC and PEC conversion of CO 2 ; many 48 reviews and book chapters exist. 6−13 In terms of sustainability 49 and process scalability, however, only a limited range of 50 candidates are worthy of serious consideration for technological 51 deployment. Thus, the use of earth-abundant and nontoxic 52 electrode materials has considerable appeal relative to noble 53 metals (e.g., Pt, Ru, Rh, etc.) or nonabundant elements (e.g., 54 Ga, In, etc.). Likewise, notwithstanding the limited solubility of 55 CO 2 in water (0.033 M at 298 K and 1 atm), the use of aqueous 56 electrolytes presents considerable practical advantages relative 57 to aprotic solvents and ionic liquids. Approaches involving 58 semiconductor suspensions and sacrificial reagents (the so-59 called "photocatalytic" (PC) processes), 14,15 while extremely 60 simple and attractive from an initial materials screening 61 perspective, will not be practical. For example, (a) the products 62

Isotopic labeling experiments were performed to better understand the electrochemical reduction of carbon dioxide on nitrogen-doped porous carbon electrodes. By using nonequilibrated solutions of selectively labeled initial carbon sources (i.e., 13CO2 and H13CO3–), bicarbonate anion was identified as the predominant source of the carbon monoxide reduction product.

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