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Evaluating spinel ferrites MFe2O4 (M = Cu, Mg, Zn) as photoanodes for solar water oxidation: prospects and limitations†
Sustainable Energy & Fuels ( IF 5.6 ) Pub Date : 2017-10-31 00:00:00 , DOI: 10.1039/c7se00448f
N. Guijarro 1, 2, 3, 4 , P. Bornoz 1, 2, 3, 4 , M. Prévot 1, 2, 3, 4 , X. Yu 1, 2, 3, 4 , X. Zhu 1, 2, 3, 4 , M. Johnson 1, 2, 3, 4 , X. Jeanbourquin 1, 2, 3, 4 , F. Le Formal 1, 2, 3, 4 , K. Sivula 1, 2, 3, 4
Affiliation  

The search for ideal semiconductors for photoelectrochemical solar fuel conversion has recently recognized the spinel ferrites as promising candidates due to their optoelectronic tunability together with superb chemical stability. However, a systematic understanding of the main material factors limiting their performance is currently lacking. Herein, nanostructured thin-film electrodes of three representative spinels, namely CuFe2O4 (CFO), MgFe2O4 (MFO) and ZnFe2O4 (ZFO), are prepared by a solution-based approach and their photoelectrochemical (PEC) properties are comprehensively characterized. Annealing post-treatments together with the deposition of NiFeOx overlayers are found to improve the native n-type response, although a dominant bulk recombination (especially in MFO) limits the saturation photocurrents (below 0.4 mA cm−2 at 1.23 V vs. RHE). Likewise, prominent Fermi level pinning due to surface states at around 0.9 V vs. RHE in all cases appears to limit the photovoltage (to ca. 300 mV). Rapid-scan voltammetry is used to gain insight into the surface states and the operation of the overlayer. Interestingly, the NiFeOx is ineffective at mitigating Fermi level pinning, but clearly participates as an electrocatalyst to improve the overall performance. Generally, these results evidence the potential and current intrinsic limitations of the spinel ferrites—establishing a roadmap for the optimization of these materials as photoanodes for solar water oxidation.

中文翻译:

评估尖晶石铁氧体MFe 2 O 4(M = Cu,Mg,Zn)作为太阳能氧化的光阳极:前景和局限性

寻求用于光电化学太阳能燃料转化的理想半导体的研究最近已经确认了尖晶石铁氧体是有希望的候选物,因为它们的光电可调性以及极好的化学稳定性。但是,目前缺乏对限制其性能的主要物质因素的系统理解。在此,通过基于溶液的方法及其光电化学法(PEC)制备了三种具有代表性的尖晶石的纳米结构薄膜电极,即CuFe 2 O 4(CFO),MgFe 2 O 4(MFO)和ZnFe 2 O 4(ZFO)。 )属性已被全面表征。退火后处理以及NiFeO x的沉积尽管主要的本体重组(尤其是在MFO中)限制了饱和光电流(在1.23 V相对于RHE的情况下低于0.4 mA cm -2),但发现叠层器可以改善固有的n型响应。同样,在所有情况下,由于相对于RHE约为0.9 V的表面状态,显着的费米能级钉扎似乎限制了光电压(至300 mV)。快速扫描伏安法用于深入了解表面状态和覆盖层的操作。有趣的是,NiFeO x在减轻费米能级钉扎方面效果不佳,但显然可以作为电催化剂参与以改善整体性能。通常,这些结果证明了尖晶石铁氧体的潜在和当前的固有局限性-建立了优化这些材料作为太阳能氧化用光阳极的路线图。
更新日期:2017-10-31
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