ith the growing importance and falling prices of renewable electricity, the issue of electricity storage to deal with the intermittent nature of renewable energy sources is becoming urgent. Storing renewable electricity in chemical bonds ('electrofuels') is particularly attractive, as it allows for high-energy-density storage and potentially high flexibility. While hydrogen is the most likely and realistic candidate for electricity storage in electrofuels, research on the electrochemical conversion of carbon dioxide and water into carbon-based fuels has intrigued electrochemists for decades, and is currently undergoing a notable renaissance [1][2][3][4] . In contrast to hydrogen production by water electrolysis, carbon dioxide electrolysis is still far from a mature technology. Significant hurdles regarding energy efficiency, reaction selectivity and overall conversion rate need to be overcome if electrochemical carbon dioxide reduction is to become a viable option for storing renewable electricity.Many electrocatalysts have been reported for the production of different compounds from the electrocatalytic carbon dioxide reduction reaction (CO 2 RR). Table 1 gives an overview of some of the most active and selective metal or metal-derived electrocatalysts towards specific products in aqueous media. The two-electron transfer products, CO and HCOOH, can be produced with low overpotential and high Faradaic efficiency on suitable electrocatalysts, but substantially higher overpotentials and lower selectivities are observed for multi-electron transfer products such as methane, ethylene and alcohols 2 . For a recent discussion about the economic perspectives of CO 2 RR, the reader is referred to a previous analysis 5 .The aim of this Review is not to be exhaustive, but rather to selectively (and subjectively) discuss some recent advances and pertinent challenges in this field, focusing on themes that have recently witnessed important progress 2,3,6,7 . An overview of some of the themes covered in this Review is shown in Fig. 1. We also discuss two important methodologies used to increase fundamental understanding of CO 2 RR: in situ spectroscopic techniques and computational techniques.

The electrochemical conversion of carbon dioxide and water into useful products is a major challenge in facilitating a closed carbon cycle. Here we report a cobalt protoporphyrin immobilized on a pyrolytic graphite electrode that reduces carbon dioxide in an aqueous acidic solution at relatively low overpotential (0.5 V), with an efficiency and selectivity comparable to the best porphyrin-based electrocatalyst in the literature. While carbon monoxide is the main reduction product, we also observe methane as by-product. The results of our detailed pH-dependent studies are explained consistently by a mechanism in which carbon dioxide is activated by the cobalt protoporphyrin through the stabilization of a radical intermediate, which acts as Brønsted base. The basic character of this intermediate explains how the carbon dioxide reduction circumvents a concerted proton–electron transfer mechanism, in contrast to hydrogen evolution. Our results and their mechanistic interpretations suggest strategies for designing improved catalysts.

A carbon supported platinum electrode in a bismuth saturated solution at a carefully chosen potential is capable of oxidizing glycerol to dihydroxyacetone with 100% selectivity. In the absence of bismuth, the primary alcohol oxidation is dominant. Using a combination of online HPLC and in situ FTIR, it is shown that Bi blocks the pathway for primary oxidation but also provides a specific Pt−Bi surface site poised for secondary alcohol oxidation.

Herein we describe a combined experimental and computational study of electrochemical glycerol oxidation in acidic media on Pt(111) and Pt(100) electrodes. Our results show that glycerol oxidation is a very structure-sensitive reaction in terms of activity and, more surprisingly, in terms of selectivity. Using a combination of online HPLC and online electrochemical mass spectrometry, we show that on the Pt(111) electrode, glyceraldehyde, glyceric acid, and dihydroxyacetone are products of glycerol oxidation, while on the Pt(100) electrode, only glyceraldehyde was detected as the main product of the reaction. Density functional theory calculations show that this difference in selectivity is explained by different binding modes of dehydrogenated glycerol to the two surfaces. On Pt(111), the dehydrogenated glycerol intermediate binds to the surface through two single Pt–C bonds, yielding an enediol-like intermediate, which serves as a precursor to both glyceraldehyde and dihydroxyacetone. On Pt(100), the dehydrogenated glycerol intermediate binds to the surface through one double PtC bond, yielding glyceraldehyde as the only product. Stripping and in situ FTIR measurements show that CO is not the only strongly bound adsorbed intermediate of the oxidation of glycerol, glyceraldehyde, and dihydroxyacetone. Although the nature of this adsorbate is still unclear, this intermediate is highly resistant to oxidation and can only be removed from the Pt surface after multiple scans.