Close to 90% Single-Pass Conversion Efficiency for CO₂ Electroreduction in an Acid-Fed Membrane Electrode Assembly

Abstract

The formation of (bi)carbonates is a pressing issue for CO2 electroreduction in neutral or alkaline solutions. It adversely causes low single-pass conversion efficiency as a result of (bi)carbonate crossover, as well as limited device lifetimes as a result of (bi)carbonate precipitation at the cathode. One emerging solution to circumvent this challenge is conducting the reaction in acids. To this end, we here demonstrate an acid-fed membrane electrode assembly (MEA) for CO2 electroreduction to CO. A diluted electrolyte with an H+ to Cs+ ratio of 1:1 and a relatively low current density are optimal conditions to achieve high CO Faradaic efficiencies. A relatively high H+ versus Cs+ ratio offers high electrocatalytic activities. By systematically evaluating the impact of H+ and Cs+ concentration on the electrochemical performance, we uncover the essential role of the balance between the rates of (bi)carbonate formation and H+ diffusion in determining the selectivity and activity. As a result, we report a CO partial current density of ∼105 mA cm–2 at an ∼4 V cell voltage, a near-doubled activity toward CO compared to a neutral MEA at a similar voltage. Under the optimal conditions for long-term operation, our acid-fed membrane electrode assembly is capable of delivering a CO Faradaic efficiency of ∼80%, an extraordinary single-pass conversion efficiency of ∼90% (about twice that of neutral MEA), and a 50 h long-term stability notably superior to those in previous reports.

Tailoring acidic microenvironments for carbon-efficient CO2electrolysis over a Ni–N–C catalyst in a membrane electrode assembly electrolyzer

“…S13b, ESI†), achieving a record in acidic CO 2 electrolysis (Table S3, ESI†). 12,13,27,29–31 In addition, the energy efficiency for CO production increases to 55% at 50 mA cm −2 and 39% at 500 mA cm −2 (Fig. 2e).…”

“…2g and Table S4, ESI †). 27,31,33 The stability of the acidic CO 2 electrolysis over Ni-N-C catalyst was first measured at an applied current density of 100 mA cm À2 using the 0.5 M K 2 SO 4 + H 2 SO 4 anolyte with pH 0.5 (Fig. S15, ESI †).…”

Ionic Blockades Control the Efficiency of Energy Recovery in Forward Bias Bipolar Membranes

“…54,55 To circumvent this issue, CO2 electrolyzers operating with acidic electrolytes (Figure 7(a)), which avoid carbonate formation, have been developed. [56][57][58][59][60][61] However, these systems universally rely on the presence of alkali metal cations in the electrolyte to engineer an alkaline pH swing local to the cathode surface. 54,56 This leads to the development of a large pH gradient between the alkaline cathode surface and the bulk acidic electrolyte, which can add a significant but oft-overlooked concentration overpotential to the overall cell voltage.…”

Surface-Immobilized Cross-linked Cationic Polyelectrolyte Enables CO2 Reduction with Metal Cation-free Acidic Electrolyte

“…9 Recently, techniques of CO 2 reduction with acidic electrolyte were developed to circumvent the asmentioned issues. [9][10][11][12][13][14][15][16][17][18][19][20][21] Alkali cations play an important role to suppress hydrogen evolution reaction (HER) and promote CO 2 reduction in acidic condition. However, alkali cations induce bicarbonate precipitation on the cathode during CO 2 reduction in acidic electrolyte, which is still an issue that hinders the sustainability of CO 2 reduction.…”