Alkaline Electrolyte and Fe Impurity Effects on the Performance and Active-Phase Structure of NiOOH Thin Films for OER Catalysis Applications

The effects of varying alkaline electrolyte
and electrolyte Fe
levels on the performance and active-phase structure of NiOOH thin
films for catalysis of the oxygen evolution reaction were studied.
An electrolyte effect on catalytic performance was observed. Under
purified conditions, current densities followed the trend Cs+ > K+ ≈ Na+ ≈ Li+ at
current densities > 1 mA/cm2. Under Fe-saturated conditions,
current densities followed the trend K+ ≈ Na+ > Cs+ > Li+ at all current densities.
Voltammetry was coupled with Raman spectroscopy for studies in LiOH
and CsOH. Raman spectra were fit to Gaussian functions and analyzed
quantitatively based on mean peak positions. Both purified and Fe-saturated
CsOH promoted slightly lower peak positions than purified and Fe-saturated
LiOH, indicating that CsOH promoted a NiOOH active-phase structure
with longer Ni–O bonds. Both Fe-saturated CsOH and LiOH promoted
slightly lower Raman peak positions than purified CsOH and LiOH, but
only for one of the two Raman peaks. These results indicate that Fe
promoted an active-phase structure with slightly longer Ni–O
bonds. This study shows that the catalytic performance and active-phase
structure of NiOOH can be tuned by simply varying the alkaline electrolyte
and electrolyte Fe levels.

本研究探究了碱性电解质（alkaline electrolyte）与电解质中铁离子浓度变化，对用于氧析出反应（oxygen evolution reaction, OER）催化的羟基氧化镍(NiOOH)薄膜的催化性能与活性相结构的影响。研究观察到电解质对催化性能存在显著影响：在纯化（无额外铁掺杂）条件下，电流密度大于1 mA/cm²时，电流密度变化趋势为Cs⁺ > K⁺ ≈ Na⁺ ≈ Li⁺；在铁饱和条件下，所有电流密度区间内的电流密度变化趋势均为K⁺ ≈ Na⁺ > Cs⁺ > Li⁺。本研究采用伏安法(voltammetry)与拉曼光谱(Raman spectroscopy)联用的表征手段，针对氢氧化锂(LiOH)与氢氧化铯(CsOH)电解质体系开展研究，拉曼光谱数据通过高斯函数(Gaussian functions)拟合，并依据平均峰位进行定量分析。相较于纯化与铁饱和的氢氧化锂体系，纯化与铁饱和的氢氧化铯体系的拉曼峰位均略低，表明氢氧化铯可诱导形成Ni-O键更长的NiOOH活性相结构；铁饱和的氢氧化铯与氢氧化锂体系的拉曼峰位相较于对应纯化体系均略低，但该现象仅出现在两个拉曼峰中的一个。上述结果表明，铁掺杂可诱导形成Ni-O键略长的活性相结构。本研究证实，仅通过调控碱性电解质种类与电解质中铁离子浓度，即可实现NiOOH催化性能与活性相结构的精准调控。