We report on the fabrication of cobalt carbide (Co 3 C) particles via a wet-chemical synthetic procedure and also describe their electrochemical oxidation to amorphous Co oxide particles that can be used as oxygen evolution reaction (OER) catalysts. Metal chalcogenide, carbide, and pnictide materials have been investigated recently, but there is some controversy regarding the composition of the actual electrocatalytic material. Carbides, in particular, have not been heavily studied as OER catalysts, and their catalytic nature is still an open question. In an effort to contribute to the clarification of the catalytic particle composition during OER, we have thoroughly characterized the elemental composition of the cobalt carbide particles at various times during OER testing and found that the particles are first converted to a transitory core−shell structure (Co 3 C core−amorphous Co oxide shell) followed by the gradual but complete conversion to an amorphous Co oxide particle during additional electrochemical OER testing. This amorphous Co oxide particle (derived from Co 3 C) maintains the shape of the original parent Co 3 C particle and exhibits a high electrochemically active surface area (ECSA). Moreover, the amorphous Co oxide particle derived from Co 3 C shows a higher geometric OER activity than either commercial Co oxide particles or Co 3 C−CoO x core−shell particles. We also observe that the fully oxidized Co 3 C shows the same intrinsic activity as commercial Co oxide particles when normalized by the ECSA. Accordingly, the amorphous Co oxide particles produced from Co 3 C possesses a porous nanostructure capable of electrocatalytically oxidizing water within the internal pores of the particles.

Gold is known currently as the most active single-element electrocatalyst for CO2 electroreduction reaction to CO. In this work, we combine Au with a second metal element, Cu, to reduce the amount of precious metal content by increasing the surface-to-mass ratio and to achieve comparable activity to Au-based catalysts. In particular, we demonstrate that the introduction of a Au-Cu bifunctional "interface" is more beneficial than a simple and conventional homogeneous alloying of Au and Cu in stabilizing the key intermediate species, *COOH. The main advantages of the proposed metal-metal bifunctional interfacial catalyst over the bimetallic alloys include that (1) utilization of active materials is improved, and (2) intrinsic properties of metals are less affected in bifunctional catalysts than in alloys, which can then facilitate a rational bifunctional design. These results demonstrate for the first time the importance of metal-metal interfaces and morphology, rather than the simple mixing of the two metals homogeneously, for enhanced catalytic synergies.

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While achieving high product selectivity is one of the major challenges of the CO2 electroreduction technology in general, Pb is one of the few examples with high selectivity that produces formic acid almost exclusively (versus H2, CO, or other byproducts). In this work, we study the mechanism of CO2 electroreduction reactions using Pb to understand the origin of high formic acid selectivity. In particular, we first assess the proton-assisted mechanism proposed in the literature using density functional calculations and find that it cannot fully explain the previous selectivity experiments for the Pb electrode. We then suggest an alternative proton-coupled-electron-transfer mechanism consistent with existing observations, and further validate a new mechanism by experimentally measuring and comparing the onset potentials for CO2 reduction vs. H2 production. We find that the origin of a high selectivity of the Pb catalyst for HCOOH production over CO and H2 lies in the strong O-affinitive and weak C-, H-affinitive characteristics of Pb, leading to the involvement of the *OCHO species as a key intermediate to produce HCOOH exclusively and preventing unwanted H2 production at the same time.

CO2 electroreduction technology is considered an important example of efficient carbon-containing energy sources. Herein, we introduce the metal–support interaction effect with a TiC support for Au/TiC electrocatalysis, which exhibits considerably enhanced activity and selectivity for electroreduction of CO2 to CO while suppressing H2 evolution. With this catalyst, an important electronic effect for CO2 electroreduction was clearly elucidated. Local sp-band charge transfer and d-band shifts play an important role in bonding with both CO and COOH adsorbates. Furthermore, the ideal surface interface between Ti and Au could inevitably maximize the electronic effect, thereby enhancing the catalytic activity of Au/TiC and subsequent CO production.