Discovery, Tuning, and Mechanistic Evaluation of Transition Metal/Group 13 Metal Electrocatalysts for Carbon Dioxide Reduction

Abstract

The anticipated negative impacts of climate change have prompted efforts to remove excess CO2 from the atmosphere, as well as prevent it from reaching the atmosphere in the first place. Following capture from point emissions sources or directly from the air, CO2 can be transformed into a diverse portfolio of carbon-containing products with both societal and economic value. Electrochemical reduction is an attractive means of converting CO2 into these products, but catalysts capable of facilitating this chemistry are plagued by large energetic requirements, poor selectivities, or limited product distributions. Of all pure-metal electrodes, only copper generates a wide distribution of highly reduced, multi-carbon products, but initial reports of bimetallic catalysts indicate the possibility of unlocking copper-like catalytic behavior using alloys.

In this work, bimetallic alloy, intermetallic, and oxide species combining non-CO2-reducing transition metals and Group 13 metals are studied for their electrocatalytic activity toward CO2, emphasizing three different areas of development: (1) catalyst discovery, (2) catalyst tuning, and (3) mechanistic evaluation. Two new electrocatalysts are shown to produce multi-carbon chemicals from CO2 and serve as formative case studies in higher-order product generation. Namely, a Cr2O3/Ga2O3 alloy produces oxalate in aqueous solution at unprecedented Faradaic efficiencies, overturning historically accepted mechanistic requirements, while the Ni3Al intermetallic serves as the first non-copper-containing electrocatalyst capable of generating three-carbon products from CO2.

Furthermore, tuning the intermetallic catalyst Ni3Ga is achieved by altering its carbon solid support and material structure. Carbon supports are demonstrated to exert morphological and surface compositional control over Ni3Ga during synthesis, thereby impacting reactivity toward CO2 during electroreduction. This sort of tuning can be exploited in catalyst design or optimization efforts, as can an understanding of CO2 reduction pathways activated by combining transition metals and Group 13 metals in electrocatalysis. Preliminary insight into this latter point is gained by studying a series of spinel oxides, which differentiate between CO- and formate-dependent CO2 reduction pathways. Ultimately, the progress reported in each of these areas of catalyst development—discovery, tuning, and mechanistic analysis—motivates ongoing CO2 conversion research and supports the goal of implementing CO2 utilization strategies for profitable environmental remediation.