Electrocatalytic reduction of carbon dioxide to carbon monoxide and methane at an immobilized cobalt protoporphyrin

Abstract

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.

Carbon Solving Carbon's Problems: Recent Progress of Nanostructured Carbon‐Based Catalysts for the Electrochemical Reduction of CO2

“…Consequently, a range of porphyrins are able to be functionalised with a range of transition metal centres (Co, Fe, Zn, Cu etc. ), [10,[79][80][81][82][83] and the resultant electrocatalysts have well-defined active centres which can be finely tuned for high activity and selectivity towards the CO 2 RR. In regards to heterogeneous electrocatalysts, the active centres are often hard to define and performance optimisation is often challenging.…”

“…[79][80][81]87,88] The preparation of these porphyrin-based materials is generally through solvothermal or hydrothermal approaches, with the resultant materials deposited on conductive substrates to form the CO 2 RR electrodes. Constructing the electrocatalysts in this way requires no high temperature steps which preserves the structure of the prophyrins and their well-defined active metal centres.…”

Reactivity of Copper Electrodes towards Functional Groups and Small Molecules in the Context of CO2 Electro-Reductions

“…Also pyridine-based co-catalysis known from Pd electrodes [37] could recently be transferred to copper-based systems [38]. Only recently, NiGa alloys have also been reported to produce trace amounts of ethene [39] and cobalt-proto-porphyrins producing methane [40].…”

Organic, Organometallic and Bioorganic Catalysts for Electrochemical Reduction of CO2

“…Methane production was achieved by reducing CO with HCHO as an intermediate. The mechanism proposed by the authors is given in Figure 17 89…”