The growing need to store increasing amounts of renewable energy has recently triggered substantial R&D efforts towards efficient and stable water electrolysis technologies. The oxygen evolution reaction (OER) occurring at the electrolyser anode is central to the development of a clean, reliable and emission-free hydrogen economy. The development of robust and highly active anode materials for OER is therefore a great challenge and has been the main focus of research. Among potential candidates, perovskites have emerged as promising OER electrocatalysts. In this study, by combining a scalable cutting-edge synthesis method with time-resolved X-ray absorption spectroscopy measurements, we were able to capture the dynamic local electronic and geometric structure during realistic operando conditions for highly active OER perovskite nanocatalysts. BaSrCoFeO as nano-powder displays unique features that allow a dynamic self-reconstruction of the material's surface during OER, that is, the growth of a self-assembled metal oxy(hydroxide) active layer. Therefore, besides showing outstanding performance at both the laboratory and industrial scale, we provide a fundamental understanding of the operando OER mechanism for highly active perovskite catalysts. This understanding significantly differs from design principles based on ex situ characterization techniques.

Extensive investigations in understanding the functional mechanisms of metal oxides behind oxygen evolution have been carried out since an electrolyzer has demonstrated promising possibilities as a device to produce hydrogen for electrochemical energy conversion systems. In particular, perovskite oxides are reputable for high activity toward the oxygen evolution reaction (OER). Here, we revisited the list of active perovskite oxides constructed based on theoretical oxygen binding energies of reaction intermediates to the catalyst surface. From this list, Ru-based perovskites, i.e. SrRuO 3 and LaRuO 3 , have been predicted as active perovskites to exhibit a particularly high OER activity. We report on the stability of nanoscaled SrRuO 3 perovskite prepared by a simple and scalable flame synthesis method. Attempts to obtain LaRuO 3 were made; however, its DFT calculated phase diagram suggests that its perovskite phase is not thermodynamically stable, which supports our experimental results such that only a mixture of different La−Ru−O phases has been obtained. Nanoscaled SrRuO 3 is evaluated for its electrochemical activity with a particular emphasis pointed toward stability in both alkaline and acidic media. Through conjoining electrochemical methods, operando X-ray absorption spectroscopy (XAS), and theoretical calculations, we show that SrRuO 3 exhibits trivial activity toward OER that decreases promptly. The loss in activity is rationalized through DFT based computations, which corroboratively suggest the poor chemical stability of both selected perovskites. Regardless of the predicted theoretical OER activity, the intrinsic instability strongly suggests that Sr-and La-based ruthenium oxides are not viable catalysts for OER in aqueous media. This further suggests that their activities are independent of their binding energies between intermediates and catalyst surface but rather closely associated with material dissolution. We highlight that understanding the origin of stability under a real operating environment is absolutely essential for the design of a sustainable electrocatalyst with optimal balance between activity and stability.

It is shown that producing PrBaCo2O5+δ and Ba0.5Sr0.5Co0.8Fe0.2O2+δ nanoparticle by a scalable synthesis method leads to high mass activities for the oxygen evolution reaction (OER) with outstanding improvements by 10× and 50×, respectively, compared to those prepared via the state-of-the-art synthesis method. Here, detailed comparisons at both laboratory and industrial scales show that Ba0.5Sr0.5Co0.8Fe0.2O2+δ appears to be the most active and stable perovskite catalyst under alkaline conditions, while PrBaCo2O5+δ reveals thermodynamic instability described by the density-functional theory based Pourbaix diagrams highlighting cation dissolution under OER conditions. Operando X-ray absorption spectroscopy is used in parallel to monitor electronic and structural changes of the catalysts during OER. The exceptional BSCF functional stability can be correlated to its thermodynamic meta-stability under OER conditions as highlighted by Pourbaix diagram analysis. BSCF is able to dynamically self-reconstruct its surface, leading to formation of Co-based oxy(hydroxide) layers while retaining its structural stability. Differently, PBCO demonstrates a high initial OER activity while it undergoes a degradation process considering its thermodynamic instability under OER conditions as anticipated by its Pourbaix diagram. Overall, this work demonstrates a synergetic approach of using both experimental and theoretical studies to understand the behavior of perovskite catalysts.

Chemosensory proteins (CSPs) are a class of small proteins expressed only in arthropods and endowed with heterogeneous functions. Some of them are involved in chemical communications, others in development or other physiological roles. The numbers of CSPs in different species of insects range from 4 in Drosophila to at least 70 in locusts, whereas in other arthropods such as crustaceans and millipedes, only 2-3 very similar sequences have been reported in each species. We have expressed, in a bacterial system, 5 of the 8 CSPs predicted by the genome of the malaria mosquito Anopheles gambiae, 4 identified at the protein level (SAP1, SAP2, SAP3, and CSP3) and a fifth annotated as part of this work, obtaining the proteins with high yields and in their soluble forms. Purified CSPs have been used to study their ligand-binding properties, both using competitive binding assays and quenching of intrinsic tryptophan fluorescence, in order to get insights into their physiological functions. The agreement between the 2 sets of data supports the assumptions that the ligands, including the fluorescent reporter, bind within the core of the proteins. Their different affinities toward a set of pure chemicals suggest specific roles in chemical communication.

The structural and electronic properties of rock salt-type Ni–Fe oxides are investigated under OER conditions. The inclusion of Fe in the rock-salt structure is shown to inhibit the transformation to more layered and disordered polymorphs.