Eggebeen Jordy J J, Koper Marc T M
Leiden Institute of Chemistry, Leiden University, PO Box 9502, 2300 RA Leiden, The Netherlands.
J Phys Chem C Nanomater Interfaces. 2025 May 30;129(23):10473-10485. doi: 10.1021/acs.jpcc.5c00649. eCollection 2025 Jun 12.
The electric double-layer at the electrode-electrolyte interface is crucial for electrocatalytic reactions in electrochemical applications, such as water splitting. On metal oxide surfaces in aqueous electrolytes, such as α-FeO(0001), proton exchange between interfacial water and surface groups (e.g., Fe-O-(H)) varies with pH and potential. This process induces pseudocapacitive charging alongside standard double-layer charging. Using impedance spectroscopy, the effect of cation concentration and pH on the adsorption pseudocapacitance originating from deprotonation of Fe-O-(H) was studied. Results show that both the double-layer capacitance and adsorption pseudocapacitance remain largely unaffected by the electrolyte concentration and pH within the 'double-layer' window. However, the charge transfer resistance ( ) was found to be inversely proportional to the NaOH concentration but remained constant between pH 12 and 14 at a fixed Na concentration. The concentration-independent double-layer capacitance suggests a Helmholtz or compact-type layer, with negligible diffuse layer contributions to the capacitance. Consequently, no diffuse layer effects are expected on the reaction kinetics, whether pseudocapacitive or Faradaic. Interestingly, the correlation between cation concentration and implies that cations mediate the proton-coupled electron transfer (PCET) acid-base reactions. This results in a cation-coupled PCET (CCPCET) mechanism that determines the current in the 'double-layer' window. Thus, the observed current in the 'double-layer' window of α-FeO(0001) is predominantly cation-mediated and pseudocapacitive rather than attributable to traditional double-layer charging.
电极 - 电解质界面处的双电层对于电化学应用中的电催化反应（如水电解）至关重要。在水性电解质中的金属氧化物表面，如α - FeO(0001)，界面水与表面基团（如Fe - O - (H)）之间的质子交换随pH值和电位而变化。这一过程在标准双电层充电的同时引发赝电容充电。利用阻抗谱，研究了阳离子浓度和pH值对源自Fe - O - (H)去质子化的吸附赝电容的影响。结果表明，在“双电层”窗口内，双电层电容和吸附赝电容在很大程度上不受电解质浓度和pH值的影响。然而，发现电荷转移电阻（ ）与NaOH浓度成反比，但在固定的Na浓度下，在pH值为12至14之间保持恒定。与浓度无关的双电层电容表明存在亥姆霍兹层或紧密型层，扩散层对电容的贡献可忽略不计。因此，无论是赝电容反应还是法拉第反应，预计扩散层对反应动力学都没有影响。有趣的是，阳离子浓度与 之间的相关性表明阳离子介导质子耦合电子转移（PCET）酸碱反应。这导致了一种阳离子耦合PCET（CCPCET）机制，该机制决定了“双电层”窗口中的电流。因此，在α - FeO(0001)的“双电层”窗口中观察到的电流主要是阳离子介导的赝电容电流，而不是归因于传统的双电层充电。
