Department of Chemistry, Queen's University , 90 Bader Lane, Kingston, Ontario K7L 3N6, Canada.
Anal Chem. 2017 Jul 18;89(14):7462-7469. doi: 10.1021/acs.analchem.7b01040. Epub 2017 Jun 29.
The electrochemical quartz-crystal nanobalance (EQCN) is an in situ technique that measures mass changes (Δm) associated with interfacial phenomena. Analysis of Δm sheds light on the mass balance (in addition to the charge and energy balances) and provides new insight into the nature of electrochemical processes. The EQCN measures changes in frequency (Δf) of a quartz-crystal resonator, which are converted into Δm using the Sauerbrey equation containing the characteristic constant (C). The value of C is determined by physical parameters of the crystal and refers to an atomically smooth surface. However, real resonators are not smooth and electrodes have their intrinsic roughness. Thus, the conversion of Δf to Δm should be done using an experimentally determined characteristic constant (C) for a given value of the surface roughness factor (R). Here, we calibrate the system using Ag electrodeposition on Pt electrodes of gradually increasing R; the latter is adjusted through Pt electrodeposition. The surface morphology of the Pt substrates prior to and after Ag electrodeposition is examined using atomic force microscopy. The values of C are determined by analyzing the slopes of charge density versus Δf plots for the Ag electrodeposition. They are different than C and increase logarithmically with R. The C and C values are used in a comparative analysis of the mass changes (δΔm) for complete cyclic voltammetry profiles covering the 0.05-1.40 V range. This reveals that the employment of C instead of C provides inaccurate values of δΔm, and the magnitude of the discrepancy increases with R.
电化学石英晶体微天平（EQCN）是一种原位技术，用于测量与界面现象相关的质量变化（Δm）。分析Δm 可以揭示质量平衡（除了电荷和能量平衡），并为电化学过程的本质提供新的见解。EQCN 测量石英晶体谐振器的频率变化（Δf），使用包含特征常数（C）的 Sauerbrey 方程将其转换为Δm。C 的值由晶体的物理参数决定，指的是原子级光滑的表面。然而，实际的谐振器并不光滑，电极具有固有粗糙度。因此，应使用实验确定的特征常数（C）将Δf 转换为Δm，对于给定的表面粗糙度因子（R）值。在这里，我们使用 Pt 电极上电沉积 Ag 来校准系统，逐渐增加 R；后者通过 Pt 电沉积来调节。使用原子力显微镜检查 Pt 基底在 Ag 电沉积前后的表面形貌。通过分析 Ag 电沉积的电荷密度与Δf 关系图的斜率来确定 C 的值。它们不同于 C，并且与 R 呈对数增加。使用 C 和 C 值对覆盖 0.05-1.40 V 范围的完整循环伏安曲线的质量变化（δΔm）进行比较分析。这表明使用 C 代替 C 会提供不准确的 δΔm 值，并且差异的大小随 R 增加而增加。
