Deciphering Electrolyte Selection for Electrochemical Reduction of Carbon Dioxide and Nitrogen to High‐Value‐Added Chemicals

Abstract

Electrochemical reduction of CO 2 (CO 2 RR) and nitrogen (NRR) constitute alternatives to fossil fuel-based technologies for the production of high-valueadded chemicals. Yet their practical application is still hampered by the low energy and Faradaic efficiencies although numerous efforts have been paid to overcome the fatal shortcomings. To date, most studies have focused on designing and developing advanced electrocatalysts, while the understanding of electrolyte, which would significantly influence the reaction microenvironment, are still not enough to provide insight to construct highly active and selective electrochemical systems. Here, a comprehensive review of the different electrolytes participating in the CO 2 RR and NRR is provided, including acidic, neutral, alkaline, and water-in-salt electrolyte as aqueous electrolytes, as well as organic electrolyte, ionic-liquids electrolyte, and the mixture of the two as non-aqueous electrolytes. Through the discussion of the roles of these various electrolytes, it is aimed to grasp their essential function during the electrochemical process and how these functions can be used as design parameters for improving electrocatalytic performance. Finally, priorities for future studies are suggested to support the in-depth understanding of the electrolyte effects and thus guide efficient selection for next-generation gasinvolving electrochemical reactions.

Molecular Imprinting Technology Enables Proactive Capture of Nitrogen for Boosted Ammonia Synthesis under Ambient Conditions

“…[20,21] On the other hand, the concentration of proton source should be controlled to be neither too high to avoid electron stealing for HER, nor too low since NRR still pertains to proton-coupled electron transfer reaction. [22,23] Considering NRR primarily occurs at the multiphase interface among gaseous nitrogen, solid electrocatalyst, and liquid electrolyte, it is better to propose the optimization strategy based on the three-phase reaction interface. [24] Mimicking key aspects of enzymatic catalysis and building microenvironments over solid catalyst surfaces may play a critical advantage in inducing the confinement effect and controlling the transport of the reactants.…”

Acid-Stable Ebonex for Continuous-Flow Nitrogen Electrofixation

“…Nitrogen electrofixaton (N 2 + 6H + + 6e → 2NH 3 ) is a viable method that can upgrade earth-abundant N 2 into useful ammonia in an aqueous electrolyte under ambient temperature and pressure, − which offers the advantages of a low carbon footprint and high energy efficiency. In comparison to those alkaline/neutral systems, the acidic nitrogen electrofixation has presented a number of remarkable features: (i) It can provide an abundant proton source directly available for participating in the reactions, without involving an additional water dissociation step (H 2 O → 2H + + OH – ), and consequently, is more energy-efficient than other counterparts. − (ii) The extremely low solubility of N 2 in aqueous solutions (0.02, at 283 K and 101 kPa) is the bottleneck of nitrogen electrofixation, which can be improved by 0.06 (pH 3) in acidic solutions (pH < 7) , because of proton–N 2 interactions. , (iii) Acidic nitrogen electrofixation can be easily integrated into a well-established proton-exchange membrane (PEM) configuration for large-scale applications. − …”

Eliminating Concentration Polarization with Cationic Covalent Organic Polymer to Promote Effective Overpotential of Nitrogen Fixation

“…[4,5] As an alternative sustainable approach, electrocatalytic nitrogen (N 2 ) reduction reaction (NRR) is becoming more and more attractive due to its mild conditions and the utilization of renewable energy sources. [6,7] Up to now, excessive attention has been focused on kinetic research, aiming to reduce the electrochemical barrier of NRR by appropriate modification of the catalyst itself, such as heteroatom doping, defect engineering, and hybrid engineering. [8][9][10] Unfortunately, the reported NRR performance still falls short of expectations, even for novel materials with low reaction barriers.…”

“…Nowadays, ammonia is predominantly synthesized by conventional Haber‐Bosch process under harsh conditions, which accounts for 1 % of the worldwide energy consumption and 1–3 % of the global CO 2 emissions [4,5] . As an alternative sustainable approach, electrocatalytic nitrogen (N 2 ) reduction reaction (NRR) is becoming more and more attractive due to its mild conditions and the utilization of renewable energy sources [6,7] . Up to now, excessive attention has been focused on kinetic research, aiming to reduce the electrochemical barrier of NRR by appropriate modification of the catalyst itself, such as heteroatom doping, defect engineering, and hybrid engineering [8–10] .…”