Formic acid reduction and CO₂ activation at Mo₂C: The important role of surface oxide

Abstract

Small organic acids, such as formic or acetic acid, which are well‐known products of the electrochemical CO2 reduction reaction, are often not further reduceable to their respective alcohols. Alcohols are well‐desired chemicals and useful as fuels, since they can be easily purified and provide a high energy density. Here, we present a combined electrochemical, differential electrochemical mass spectrometry (DEMS), and nuclear magnetic resonance spectroscopy (NMR) study, providing insight in the electro‐reduction of formic acid on Mo2C electrodes, and the corresponding formation of notable amounts of methanol, with a Faraday efficiency of ∼27 % at a high steady state current density of –0.3 mA/cm2 compared to other formic acid electroreduction catalysts, such as Pb or Sn. Intriguingly, we find that formic and acetic acid readily form on native oxide covered Mo2C surfaces in air and especially in humid CO2 atmosphere. We realize that the thin native oxide layer that is ubiquitously present on these electrodes is the key factor for the activation of CO2 and the corresponding formation of formic and acetic acid at the solid/gas interface. Subsequent electrochemical reduction of these two acids at the solid/liquid interface proceeds through direct formation of their respective alcohols. The activity toward organic acid reduction on Mo2C catalysts can therefore be enhanced by their adsorption properties at the surface and not necessarily through inhibition of the HER, which is exceptional and points to a general strength of compound catalysts for organic acid reduction and CO2 activation.

The Relevance of the Interfacial Water Reactivity for Electrochemical CO Reduction on Copper Single Crystals

“…For all experiments, a PEEK flow cell (Hiden Analytical, U.K.) with a constant electrolyte flow rate of 50 μL min –1 was used. Further information on the setup and the delay time can be found elsewhere. − A Metrohm Autolab (PGSTAT 302N) was used as potentiostat. The scan rate was 2 mV s –1 , and the m / z signals of 2 (hydrogen, H 2 + ), 15 (methane, CH 3 + ) and 26 (ethylene, C 2 H 2 + ) were simultaneously recorded.…”

Electroreduction of CO2 in a Non-aqueous Electrolyte─The Generic Role of Acetonitrile

“…The polycrystalline electrocatalyst was synthesized according to previous publications. , Here, Mo (99.95%, Advent Ltd.) carburization was performed in a home-built, vacuum-assisted quartz furnace, which allows the transfer of electrodes into the glovebox under a H 2 atmosphere after the synthesis.…”

Electrochemically decoupled reduction of CO2 to formate over a dispersed heterogeneous bismuth catalyst enabled via redox mediators

“…40 It has, however, been reported that on select catalysts, formic acid can be reduced to methanol, albeit with low current density and poor selectivity. [41][42][43] The primary difficulty with formate/formic acid as a product is the need for intricate separation procedures, which is further complicated in the decoupled system by the redox meditator. It is desirable for the mediator to be indefinitely reusable in a semi-closed system where only CO 2 and water are added and products are collected.…”