Promoting Cu-catalysed CO2 electroreduction to multicarbon products by tuning the activity of H2O

Abstract

The electrochemical reduction of CO2 to multi-carbon products is a sustainable route for the synthesis of energy dense chemical feedstocks. Cu is the only material known to produce multi-carbon (C2+) products with appreciable selectivity. However, the generation of C2+ products compete with the formation of C1 products and the reduction of H2O to hydrogen. Here, we tuned the activity of H2O from 0.97 to 0.47 by using a NaClO4-based H2O-in-salt-electrolyte. Commercial Cu-nanoparticle electrodes evaluated in pH 9 NaClO4 with a H2O activity of 0.66 achieved a Faradaic Efficiency of ~ 73% for C2+ products (ethylene, ethanol, and propanol) with a C2+ partial current density of −110 mA cm -2 at -0.88 vs. Reversible Hydrogen Electrode. Furthermore, we were able to modulate the C2+/C1 ratios between 1 to 20 by altering only the H2O activity, demonstrating unrivaled tunability between C1 and C2+ products. Analysis of the Tafel slopes and reaction orders on model Cu electrodes revealed that the mechanism for forming C2 products was unchanged across a wide range of H2O activities, while C1 products and H2 had mechanisms which changed as the activity of H2O was lowered. Therefore, we can conclude that protons are part of the rate-determining step for the formation of C1 products, but not C2 products. We have demonstrated that tuning the activity of H2O in an aqueous solvent is a powerful new guiding principle for improving the reduction of CO2 to C2 and C3 products.

SiO2 assisted Cu0–Cu+–NH2 composite interfaces for efficient CO2 electroreduction to C2+ products

“…The high coverage of *H ad species can enhance the protonation process of C 2+ intermediates and desorption of products, thus promoting the efficient formation of C 2+ products from the CO 2 RR process. 50,51…”

Thermodynamic, Kinetic, and Transport Contributions to Hydrogen Evolution Activity and Electrolyte-Stability Windows for Water-in-Salt Electrolytes

“…The approach developed here, combining different measurements to understand how transport, kinetics, and thermodynamics together modulate rates of interface electrochemical processes in electrolytes, and thus the practically relevant electrolyte-stability window, is of broad utility in understanding fundamental aspects of, and design rules for, advanced aqueous electrolytes more broadly. Beyond battery applications, the reported understanding of WiSEs and related advanced electrolytes may be of substantial interest to fields like electrochemical CO 2 and N 2 reduction, where the HER is also a parasitic reaction and precise interface microenvironment control is key to progress. ,,− …”

“…Beyond battery applications, the reported understanding of WiSEs and related advanced electrolytes may be of substantial interest to fields like electrochemical CO 2 and N 2 reduction, where the HER is also a parasitic reaction and precise interface microenvironment control is key to progress. 25…”

“…Despite the tremendous effort in developing WiSEs that aim to offer high-voltage/high-energy batteries, the understanding of stability/instability in WiSEs is constrained by the limited research on the individual effects of thermodynamic and kinetic factors from HER and OER . It has been largely accepted, but without much direct proof, that a scarcity of free water molecules with reduced thermodynamic activity widens the overall voltage window, and the creation of a protective solid–electrolyte interphase (SEI) layer at the negative electrode may further modulate kinetics. , Beyond battery applications, WiSEs are being used as advanced electrolytes for electrosynthesis, for example in CO 2 electroreduction where controlling the apparent “activity” of water affects the selectivity and product distributions. − …”

Insight on Atomically Dispersed Cu Catalysts for Electrochemical CO2 Reduction

“…They not only have AD active centers and unsaturated coordination structures but also have the intrinsic properties of metal Cu. ,, Moreover, they can ignore the negative effects of morphology, valence, and crystallographic properties on the selectivity of C 2+ products. ,, Nevertheless, it is still difficult for AD Cu catalysts to achieve high selectivity for specific C 2+ products. Fortunately, some effective strategies have been put forward, such as increasing local *CO concentration, shortening the distance of sites, constructing dual active sites to accelerate CO 2 reduction and H 2 O dissociation, , etc., which promote C–C coupling by adjusting *CO adsorption behavior/surface coverage or/and modulating *H coverage or/and accelerating the generation of key intermediates.…”