Electrocatalytic reactions occur in the nanoscale space at the electrified electrode–electrolyte interface. It is well known that the electrode–electrolyte interface, also called as interfacial microenvironment, is difficult to investigate due to the interference of bulk electrolytes and its dynamic evolution in response to applied bias potential. Here, we employ electrochemical co-reduction of CO2 and H2O on commercial Ag electrodes as a model system, in conjunction with quaternary ammonium cationic surfactants as electrolyte additives. We probe bias-potential-driven dynamic response of the interfacial microenvironment as well as the mechanistic origin of catalytic selectivity. By virtue of comprehensive in situ vibrational spectroscopy, electrochemical impedance spectroscopy, and molecular dynamics simulations, it is revealed that the structure of surfactants is dynamically changed from a random distribution to a nearly ordered assembly with increasing bias potential. The nearly ordered surfactant assembly regulates the interfacial water environment by repelling isolated water and suppressing water orientation into an ordered structure as well as promotes CO2 enrichment at the electrified interface. Eventually, the formed hydrophobic–aerophilic interface microenvironment reduces the activity of water dissociation and increases the selectivity of CO2 electroreduction to CO. These results highlight the importance of regulating the interfacial microenvironment by organic additives as a means of boosting the electrochemical performance in electrosynthesis and beyond.
Electrochemical alkynol semi-hydrogenation has emerged as a sustainable and environmentally benign route for the production of high-value alkenols, featuring water as the hydrogen source instead of H2. It is highly challenging to design the electrode–electrolyte interface with efficient electrocatalysts and their matched electrolytes to break the selectivity-activity stereotype. Here, boron-doped Pd catalysts (PdB) and surfactant-modified interface are proposed to enable the simultaneous increase in alkenol selectivity and alkynol conversion. Typically, compared to pure Pd and commercial Pd/C catalysts, the PdB catalyst achieves both higher turnover frequency (139.8 h–1) and specific selectivity (above 90%) for the semi-hydrogenation of 2-methyl-3-butyn-2-ol (MBY). Quaternary ammonium cationic surfactants that are employed as electrolyte additives are assembled at the electrified interface in response to applied bias potential, establishing an interfacial microenvironment that can facilitate alkynol transfer and hinder water transfer suitably. Eventually the hydrogen evolution reaction is inhibited and alkynol semi-hydrogenation is promoted, without inducing the decrease of alkenol selectivity. This work offers a distinct perspective on creating a suitable electrode–electrolyte interface for electrosynthesis.
Copper (Cu)‐based metal–organic frameworks (MOFs) and MOF‐derived catalysts are well studied for electroreduction of carbon dioxide (CO2); however, the effects of organic linkers for the selectivity of CO2 reduction are still unrevealed. Here, a series of Cu‐based MOF‐derived catalysts is investigated with different organic linkers appended, named X‐Cu‐BDC (BDC = 1,4‐benzenedicarboxylic acid, X = NH2, OH, H, F, and 2F). It is found that the linkers affect the faradaic efficiency (FE) for C2 products with an order of NH2 < OH < bare Cu‐BDC < F < 2F, thus tuning the FEC2:FEC1 ratios from 0.6 to 3.8. As a result, the highest C2 FE of ≈63% at a current density of 150 mA cm−2 on 2F‐Cu‐BDC derived catalyst is achieved. Using operando Raman measurements, it is revealed that the MOF derives to Cu2O during eCO2RR but organic linkers are stable. The fluorine group in organic linker can promote the H2O dissociation to *H species, further facilitating the hydrogenation of *CO to *CHO that helps CC coupling.
Designing highly efficient and stable electrode‐electrolyte interface for hydrogen peroxide (H2O2) electrosynthesis remains challenging. Inhibiting the competitive side reaction, 4 e− oxygen reduction to H2O, is essential for highly selective H2O2 electrosynthesis. Instead of hindering excessive hydrogenation of H2O2 via catalyst modification, we discover that adding a hydrogen‐bond acceptor, dimethyl sulfoxide (DMSO), to the KOH electrolyte enables simultaneous improvement of the selectivity and activity of H2O2 electrosynthesis. Spectral characterization and molecular simulation confirm that the formation of hydrogen bonds between DMSO and water molecules at the electrode‐electrolyte interface can reduce the activity of water dissociation into active H* species. The suitable H* supply environment hinders excessive hydrogenation of the oxygen reduction reaction (ORR), thus improving the selectivity of 2 e− ORR and achieving over 90 % selectivity of H2O2. This work highlights the importance of regulating the interfacial hydrogen‐bond environment by organic molecules as a means of boosting electrochemical performance in aqueous electrosynthesis and beyond.
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