Dramatic HER Suppression on Ag Electrodes via Molecular Films for Highly Selective CO₂ to CO Reduction

Abstract

The carbon dioxide reduction reaction (CO2RR) in aqueous electrolytes suffers from efficiency loss due to the competitive hydrogen evolution reaction (HER). Developing efficient methods to suppress HER is a crucial step toward CO2 utilization. Herein, we report the selective conversion of CO2 to CO on planar silver electrodes with Faradaic efficiencies >99 % using simple pyridinium-based additives. Similar to our previous studies on copper electrodes, the additives form an organic film which alters CO2RR selectivity. We report electrochemical kinetic and other mechanistic data to shed light on the role of these organic layers in suppressing HER. These data suggest that hydrogen production is selectively inhibited by the growth of a hydrophobic organic layer on the silver surface that limits proton but not CO2 mass transport at certain applied potentials. The data also point to the involvement of a proton-transfer within the rate determining step of the catalysis, instead of the commonly observed electron-transfer step for the case of planar Ag electrodes.

Customizing the microenvironment of CO2 electrocatalysis via three‐phase interface engineering

“…Pyridinium‐based organic film can limit proton but not CO 2 mass transport (Figure 3C). 50 It was found that the limiting effects depends on the applied potentials: when the potentials locate between −1.0 and −1.2 V, the hydrophobic layer on the Ag electrode surface can selectively limit proton transport but not CO 2 . Zhang et al 51 fabricated a core‐shell carbon layer as the hydrophobic interface to alter Cu CRR selectivity.…”

Resolving local reaction environment toward an optimized CO2-to-CO conversion performance

“…Under aqueous CO 2 RR operation conditions, the hydrated cations will be migrated to the cathode, for which the cation identity and the resultant interfacial electric field are known with a significant impact on the activity of desired products. [20][21][22] More recently, Peters et al reported the surface modification of a hydrophobic pyridinium layer on Ag that limits the diffusion rate of proton carriers but not CO 2 , thus delivering a CO selectivity above 99% at À0.99 V. 23 To directly probe the interactions of reactive species with their liquid reaction environment, developing operando methodologies and techniques are highly important but challenging to capture the real-time information on CO 2 reduction reactants, products, adsorbates and interfacial species evolution. 24,25 Intermittent online gas chromatography (GC) 26 and ex situ 1 H nuclear magnetic resonance (NMR) 27 are the two most widely adopted techniques for the quantification of gaseous and dissolved liquid products, respectively, providing an ex parte piece for this puzzle.…”

Nanostructure@metal-organic frameworks (MOFs) for catalytic carbon dioxide (CO2) conversion in photocatalysis, electrocatalysis, and thermal catalysis

“…The surface coordination number of Cu clusters was judiciously controlled thus leading to a promoted catalytic selectivity, activity as well as efficiency for CO 2 RR. The Faradaic efficiency (FE) of C 2 H 4 production reached a record 45% for MOF-tuned Cu cluster catalysts [89]. The organic film such as pyridinium-based additives was also confirmed to greatly promote the selectivity of Ag and Cu up to >99% Faradaic efficiencies for electrocatalytic CO 2 RR, which is also shedding light on the design of metal@MOF CO 2 electrocatalysts [90].…”