Electrocatalytic conversion of CO₂ to produce solar fuels in electrolyte or electrolyte-less configurations of PEC cells

Abstract

The electrocatalytic reduction of CO2 is studied on a series of electrodes (based on Cu, Co, Fe and Pt metal nanoparticles deposited on carbon nanotubes or carbon black and then placed at the interface between a Nafion membrane and a gas-diffusion-layer electrode) on two types of cells: one operating in the presence of a liquid bulk electrolyte and the other in the absence of the electrolyte (electrolyte-less conditions). The results evidence how the latter conditions allow productivity of about one order of magnitude higher and how to change the type of products formed. Under electrolyte-less conditions, the formation of >C2 products such as acetone and isopropanol is observed, but not in liquid-phase cell operations on the same electrodes. The relative order of productivity in CO2 electrocatalytic reduction in the series of electrodes investigated is also different between the two types of cells. The implications of these results in terms of possible differences in the reaction mechanism are commented on, as well as in terms of the design of photoelectrocatalytic (PEC) solar cells.

CO2 Reduction of Hybrid Cu2O–Cu/Gas Diffusion Layer Electrodes and their Integration in a Cu‐based Photoelectrocatalytic Cell

“…A GDL was used as the support for depositing copper because it allows operating the reduction of CO 2 with or without a liquid electrolyte. Different behaviors in CO 2 reduction could be obtained in the two cases, even using the same electrolyte, owing to different surface concentrations of CO 2 and the absence of the electrolyte in the second case . This electrode configuration allows also the introduction of elements for CO 2 capture in the GDL to enhance the surface concentration of CO 2 on the electrocatalyst, which favors the formation of >C 1 products during the electroreduction of CO 2 .…”

“…We also comment that in principle the use of in situ/operando spectroscopic methods should be used to unravel the reaction mechanism. However, we earlier showed that the formation of acetate in the electrocatalytic reduction of CO 2 is strongly dependent on the effective surface concentration of CO 2 at the electrocatalyst surface, rather than depending only on the nature of the electrocatalyst itself . In addition, changing the electrode characteristics, for example going from a GDL‐type electrode as used here to a conventional electrode, although using the same electrocatalyst, the type of species of CO 2 reduction change significantly.…”

“…Different behaviors in CO 2 reduction could be obtainedi nt he two cases, even using the same electrolyte, owing to different surface concentrations of CO 2 and the absence of the electrolyte in the second case. [51] This electrode configuration allows also the introduction of elements for CO 2 capturei nt he GDL to enhance the surfacec oncentration of CO 2 on the electrocatalyst, which favors the formation of > C 1 products during the electroreduction of CO 2 . [52] However, operations in the presence of an electrolyte are the most commonly reported in literature, so we selected here to operate in the presence of an electrolyte to allow ab etter comparison with other results.…”

Electrolyte-less design of PEC cells for solar fuels: Prospects and open issues in the development of cells and related catalytic electrodes

“…This result, further commented below, well evidences that under EL-conditions, a different type of performances to those obtained under operations in the presence of a liquid electrolyte could be obtained. In a recent paper [164] the electrocatalytic reduction of CO 2 was studied on a series of electrodes on two types of cells: one operating in the presence of a liquid bulk electrolyte and the other in the absence of the electrolyte (EL-conditions). The results evidence how the latter conditions allow about one order of magnitude higher productivity and to change the type of products formed.…”

Solar Production of Fuels from Water and CO2: Perspectives and Opportunities for a Sustainable Use of Renewable Energy

“…Operations without a bulk electrolyte (electrolyte-less conditions, EL) may greatly help to develop PEC solar cells for high temperature operations [126]. Interesting indications, on both the limiting steps of the process and the reaction mechanism, have been obtained comparing CO 2 reduction performed on the same electrodes in the presence (liquid-phase) or absence (gas-phase) of a bulk electrolyte.…”