Mechanism of Cations Suppressing Proton Diffusion Kinetics for Electrocatalysis

Abstract

Proton transfer is crucial for electrocatalysis. Accumulating cations at electrochemical interfaces can alter the proton transfer rate and then tune electrocatalytic performance. However, the mechanism for regulating proton transfer remains ambiguous. Here, we quantify the cation effect on proton diffusion in solution by hydrogen evolution on microelectrodes, revealing the rate can be suppressed by more than 10 times. Different from the prevalent opinions that proton transport is slowed down by modified electric field, we found water structure imposes a more evident effect on kinetics. FTIR test and path integral molecular dynamics simulation indicate that proton prefers to wander within the hydration shell of cations rather than to hop rapidly along water wires. Low connectivity of water networks disrupted by cations corrupts the fast‐moving path in bulk water. This study highlights the promising way for regulating proton kinetics via a modified water structure.

Accelerating the Reaction Kinetics of CO2 Reduction to Multi‐Carbon Products by Synergistic Effect between Cation and Aprotic Solvent on Copper Electrodes

“…To better understand the effect of Na + and DMSO molecules on the microstructure following their addition to the water structure, we extracted the average coordination number (CN) of hydrogen bonds surrounding one water molecule from the AIMD simulation trajectories (Figure 2b, Figures S3 and S4). In contrast to H 2 O system, we found that the average CN of hydrogen bonds follows the order of H 2 O>Na‐H 2 O>DMSO>Na‐DMSO, clearly indicating that adding a cation slightly reduces water network connectivity, [8d,11] which decreases even further with the addition of DMSO. Subsequently, we analyzed the coordination of Na + and DMSO with the oxygen atom from surrounding water.…”

“…To achieve this strategy, we propose that functionalized electrolytes could effectively regulate the C−C coupling and hydrogenation process. Previous studies have shown that alkali metal cations not only play a role in promoting C−C coupling, but also show promise in decreasing water network connectivity [8d] . Nevertheless, it may not be sufficient to effectively inhibit HER due to the formation of a narrow H‐transfer gap, as shown in Figure 1a.…”

Interfacial Micro‐Environment of Electrocatalysis and Its Applications for Organic Electro‐Oxidation Reaction

“…Additionally, more in‐depth and broadened understanding of the conventional concept of IME is needed. For instance, in accordance with the updated investigation on cation effect by Sun et al., [ 211 ] the accumulated cations at the electrochemical interface regulated the proton transfer rate via changing water structure, rather than the prevalent viewpoints of modifying electric field.…”

Electric Double Layer Effects in Electrocatalysis: Insights from Ab Initio Simulation and Hierarchical Continuum Modeling

“…The proposed H-bond network connectivity mechanism has also been used to understand the cation effect in hydrogen electrocatalytic kinetics. Recently, Li et al found that on Au and Pt microelectrodes in 0.1 M trifluoromethanesulfonic acid (HOTf), the diffusion-limited current of HER was suppressed greatly as KOTf was added to the solution, which means that the proton transfer rate in the EDL was much lowered by the existence of K + cations . Combined with the ab initio path integral molecular dynamics simulation and the graph theory approach, they have simulated the proton diffusion in the acid solutions without and with K + and evaluated the connectivity of H-bond networks (Figure g,h).…”