Marsh Paul, Huang Mao-Hsiang, Xia Xing, Tran Ich, Atanassov Plamen, Cao Hung
Department of Electrical Engineering and Computer Science, University of California Irvine, Irvine, CA 92697, USA.
Irvine Materials Research Institute, University of California Irvine, Irvine, CA 92697, USA.
Sensors (Basel). 2024 Feb 1;24(3):962. doi: 10.3390/s24030962.
Electrodeposited amorphous hydrated iridium oxide (IrOx) is a promising material for pH sensing due to its high sensitivity and the ease of fabrication. However, durability and variability continue to restrict the sensor's effectiveness. Variation in probe films can be seen in both performance and fabrication, but it has been found that performance variation can be controlled with potentiostatic conditioning (PC). To make proper use of this technique, the morphological and chemical changes affecting the conditioning process must be understood. Here, a thorough study of this material, after undergoing PC in a pH-sensing-relevant potential regime, was conducted by voltammetry, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Fitting of XPS data was performed, guided by raw trends in survey scans, core orbitals, and valence spectra, both XPS and UPS. The findings indicate that the PC process can repeatably control and conform performance and surface bonding to desired calibrations and distributions, respectively; PC was able to reduce sensitivity and offset ranges to as low as ±0.7 mV/pH and ±0.008 V, respectively, and repeat bonding distributions over ~2 months of sample preparation. Both Ir/O atomic ratios (shifting from 4:1 to over 4.5:1) and fitted components assigned hydroxide or oxide states based on the literature (low-voltage spectra being almost entirely with suggested hydroxide components, and high-voltage spectra almost entirely with suggested oxide components) trend across the polarization range. Self-consistent valence, core orbital, and survey quantitative trends point to a likely mechanism of ligand conversion from hydroxide to oxide, suggesting that the conditioning process enforces specific state mixtures that include both theoretical Ir(III) and Ir(IV) species, and raising the conditioning potential alters the surface species from an assumed mixture of Ir species to more oxidized Ir species.
电沉积非晶态水合氧化铱（IrOx）因其高灵敏度和易于制备而成为一种很有前景的pH传感材料。然而，耐久性和可变性仍然限制着传感器的有效性。在性能和制备过程中都可以看到探针膜的变化，但已经发现通过恒电位调节（PC）可以控制性能变化。为了正确使用该技术，必须了解影响调节过程的形态和化学变化。在此，通过伏安法、扫描电子显微镜（SEM）、能量色散X射线光谱（EDS）、X射线衍射（XRD）和X射线光电子能谱（XPS）对该材料在与pH传感相关的电位范围内进行PC处理后进行了深入研究。在XPS和UPS的测量扫描、核心轨道和价光谱的原始趋势指导下，对XPS数据进行了拟合。研究结果表明，PC过程可以分别将性能和表面键合可重复地控制并符合到所需的校准和分布；PC能够将灵敏度和偏移范围分别降低至±0.7 mV/pH和±0.008 V，并在约2个月的样品制备过程中重复键合分布。Ir/O原子比（从4:1转变为超过4.5:1）以及根据文献指定为氢氧化物或氧化物状态的拟合成分（低电压光谱几乎完全是建议的氢氧化物成分，高电压光谱几乎完全是建议的氧化物成分）在整个极化范围内都有变化趋势。自洽的价态、核心轨道和测量定量趋势表明可能存在从氢氧化物到氧化物的配体转化机制，这表明调节过程强制形成特定的状态混合物，其中包括理论上的Ir(III)和Ir(IV)物种，并且提高调节电位会使表面物种从假定的Ir物种混合物转变为氧化程度更高的Ir物种。
