Electrocatalyst Microenvironment Engineering for Enhanced Product Selectivity in Carbon Dioxide and Nitrogen Reduction Reactions

Abstract

Carbon and nitrogen fixation strategies are regarded as alternative routes to produce valuable chemicals used as energy carriers and fertilizers that are traditionally obtained from unsustainable and energy-intensive coal gasification (CO and CH 4 ), Fischer−Tropsch (C 2 H 4 ), and Haber−Bosch (NH 3 ) processes. Recently, the electrocatalytic CO 2 reduction reaction (CO 2 RR) and N 2 reduction reaction (NRR) have received tremendous attention, with the merits of being both efficient strategies to store renewable electricity while providing alternative preparation routes to fossil-fuel-driven reactions. To date, the development of the CO 2 RR and NRR processes is primarily hindered by the competitive hydrogen evolution reaction (HER); however, the corresponding strategies for inhibiting this undesired side reaction are still quite limited. Considering such complex reactions involve three gas−liquid−solid phases and successive proton-coupled electron transfers, it appears meaningful to review the current strategies for improving product selectivity in light of their respective reaction mechanisms, kinetics, and thermodynamics. By examining the developments and understanding in catalyst design, electrolyte engineering, and three-phase interface modulation, we discuss three key strategies for improving product selectivity for the CO 2 RR and NRR: (i) targeting molecularly defined active sites, (ii) increasing the local reactant concentration at the active sites, and (iii) stabilizing and confining product intermediates.

Double-Atom Catalysts Featuring Inverse Sandwich Structure for CO2 Reduction Reaction: A Synergetic First-Principles and Machine Learning Investigation

“…The free energy G for each step in the whole CO 2 RR was calculated according to the computational hydrogen electrode (CHE) model proposed by Nørskov and coworkers . Despite its known weaknesses and limitations, the CHE model continues to find widespread applications in the field of electrocatalysis research. ,,, According to the CHE model, the effect of electrode potential ( U ) and electrolyte acidity (pH) on CO 2 RR can be considered as an energy shift of the free energy change in the electrochemical step: Δ G U = – eU ; Δ G pH = RT ln 10 × pH where R is the gas constant, and pH was set as zero in this study to mimic the acidic condition. The limiting potential ( U L ) was defined as the maximum free energy change (Δ G max ) among neighboring elementary steps along the most favorable pathway: U L = – Δ G max / e , where Δ G max is the free energy of the potential-limiting step .…”

A Bi‐Co Corridor Construction Effectively Improving the Selectivity of Electrocatalytic Nitrate Reduction toward Ammonia by Nearly 100%

“…[ 4,5 ] The Haber−Bosch (H−B) process currently contributes 90% of the world's NH 3 production, but it also consumes 2% of the energy produced by humans, fueling massive fossil fuels that produce 400 Mt of carbon dioxide emissions per year. [ 6–9 ] Therefore, a clean, efficient and sustainable new NH 3 production method is urgently needed to replace the H−B process of high energy consumption and pollution. Electrocatalytic synthesis of NH 3 utilizing renewable energy can basically meet the above needs, which has become the front domain and research focus recently.…”

Insight into the Role of Entropy in Promoting Electrochemical CO2 Reduction by Imidazolium Cations

“…Achieving net-zero carbon emissions requires technologies for the long-term storage of renewable electricity and the sustainable synthesis of chemicals. The electrochemical reduction of CO 2 (CO 2 RR) to C1 and C2 carbon feedstocks has the potential to fulfill these needs and has, consequently, received great interest in recent decades. − Considerable progress has been achieved in understanding the mechanism of CO 2 RR. − Surprisingly, however, the most fundamental question of how the applied potential controls the rate of the CO 2 RR has not been conclusively answered. Basic electron transfer models such as the Tafel, Butler–Volmer, and simple Marcus models assume that the applied potential controls reaction rates by modulating the height of the activation barrier (Figure a). − In this picture, ambient heat ( k B T ) provides the energy needed to surmount the activation barrier, while the presence of an electrocatalyst and cocatalyst modifies its height.…”