Pseudobrookite (Fe2TiO5) has attracted significant attention as an emerging photoanode for water oxidation due to reports of enhanced performance in polycrystalline heterostructures with α-Fe2O3 or TiO2. However, the specific properties and contribution of Fe2TiO5 remain unknown. Here, we present the first photoelectrochemical characterization of epitaxial thin film Fe2TiO5, an ideal platform for probing the inherent response of this earth-abundant photoanode for solar water splitting. Moreover, by using an electrolyte containing a hole scavenger, we find highly efficient charge transfer at the Fe2TiO5–electrolyte interface. This notable surface property is exploited in the form of an Fe2TiO5/α-Fe2O3 heterostructure photoanode, for which we observe a photocurrent density increase by 1 order of magnitude and an onset potential improvement by ∼300 mV. Establishing these fundamental properties elucidates the nature of reaction mechanisms on Fe2TiO5 and informs the design of highly efficient water photo-oxidation devices by incorporating this material with other photoanodes.

The growing demands for high-energy density electrical energy storage devices stimulate the coupling of conversion-type cathodes and lithium (Li) metal anodes. While promising, the use of these “Li-free” cathodes brings new challenges to the Li anode interface, as Li needs to be dissolved first during cell operation. In this study, we have achieved a direct visualization and comprehensive analysis of the dynamic evolution of the Li interface. The critical metrics of the interfacial resistance, Li growth, and solid electrolyte interface (SEI) distribution during the initial dissolution/deposition processes were systematically investigated by employing multidimensional analysis methods. They include three-electrode impedance tests, in situ atomic force microscopy, scanning electrochemical microscopy, and cryogenic scanning transmission electron microscopy. The high-resolution imaging and real-time observations show that a loose, diffuse, and unevenly distributed SEI is formed during the initial dissolution process. This leads to the dramatically fast growth of Li during the subsequent deposition, deviating from Fick’s law, which exacerbates the interfacial impedance. The compactness of the interfacial structure and enrichment of electrolyte species at the surface during the initial deposition play critical roles in the long-term stability of Li anodes, as revealed by operando confocal Raman spectroscopic mapping. Our observations relate to ion transfer, morphological and structural evolution, and Li (de)solvation at Li interfaces, revealing the underlying pathways influenced by the initial dissolution process, which promotes a reconsideration of anode investigations and effective protection strategies.

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A major focus of anion exchange membrane fuel cell (AEMFC) research revolves around the study of the performance and degradation of the catalyst layer structure [1]. This complex structure typically consists of catalyst nanoparticles, such as platinum, loaded onto a carbon support along with a dispersion of polymeric ionomer. The interactions between the catalyst-loaded carbon particles and the ionomer have a direct impact on both the ionic and electronic conductivity in the catalyst layer [2,3]. A robust approach to characterize the distribution of ionomer in the catalyst layer is therefore important to advance our understanding of fuel cell performance. Here, we show that low-dose cryo-TEM imaging enables direct imaging of the ionomer and its distribution in the catalyst layer of AEMFCs.