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For electrocatalysts of oxygen evolution reaction (OER), a new accelerated durability test (ADT) protocol is presented. The protocol is designed to closely mimic the fluctuations of renewable energies. The unit cycle of the current ADT protocol represents the "ON / OFF" operation mode. In the "ON" step, the electrolyzer operates under a DC current of 0.6 A cm-2. In the "OFF" step, the electrocatalyst is subjected to a constant potential that is clearly more cathodic than its OER onset potential (namely, 0.3, 0.5, and 0.7 V vs. RHE) for 10 or 60 s. The transition from the "ON" state to the "OFF" state occurs through a cathodic linear sweep voltammetry of a fast sweep rate to mimic the sudden changes in the renewable power. A NiCoO x /Ni-mesh electrode was used as a case study. The electrode showed remarkable durability under continuous operation (i = 0.6 A cm-2) for about 900 hours. However, it did suffer severe degradation after a certain number of ADT cycles, and the rate of degradation mainly depends on the potential value and the duration of the "OFF" step. Interestingly, the inclusion of the 10-sec open-circuit potential step after the "ON" step clearly mitigates the impact of energy fluctuations on the durability of OER electrocatalysts.

Solar water splitting is an alternative way of clean and sustainable hydrogen production. Tantalum nitride (Ta 3 N 5 ) is one of the promising candidates that recently attracted a great amount of attention as photoelectrodes for solar water splitting. Nevertheless, it suffers severely from photocorrosion in an aqueous solution. Therefore, the precise selection of a cocatalyst, in terms of the material, the amount, and the way of its deposition, is indispensable to highly improve its water splitting performance. In the present work, we introduce a Fe−Ni−Co mixed-metal oxide as a water oxidation cocatalyst that remarkably improved the photocurrent and photostability of the pristine Ta 3 N 5 photoanode. The cocatalyst-modified electrode showed a photocurrent of about 4.0 mA cm −2 at 1.23 V vs RHE in 1 M NaOH. The electrode maintained 100% and 96% of the initial photocurrent after irradiation times of 1 and 2 h, respectively. In addition, a continuous evolution of hydrogen and oxygen occurred for 2 h at quantitative Faraday efficiencies (>96%). This photostability is superior compared to that of the other singlelayer modified Ta 3 N 5 photoanodes reported so far. It is noteworthy that the anodic spark deposition is used to fabricate precursor electrodes (NaTaO 3 ), which then were converted to Ta 3 N 5 by nitridation in an ammonia atmosphere.

The semidirect x-ray photoelectron spectroscopy technique was used to measure the band alignments at the interface of heterostructures based on SnS. The layers were deposited by electrochemical deposition (ECD), chemical bath deposition (CBD), or photochemical deposition (PCD). The following four kinds of heterojunctions were characterized. (1) ECD-SnS/PCD-CdS. (2) CBD-SnS/PCD-CdS. (3) ECD-SnS/ECD-InSxOy. (4) CBD-SnS/ECD-InSxOy. The valence band offsets ΔEV of those four heterojunctions are determined to be 1.34, 1.59, 0.77, and 0.74±0.3 eV, respectively.