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Copper oxides are promising photocathode materials for solar hydrogen production due to their narrow optical band gap energy allowing broad visible light absorption. However, they suffer from severe photocorrosion upon illumination, mainly due to copper reduction. Nanostructuring has been proven to enhance the photoresponse of CuO photocathodes; however, there is a lack of precise structural control on the nanoscale upon sol-gel synthesis and calcination for achieving optically transparent CuO thin film photoabsorbers. In this study, nanoporous and nanocrystalline CuO networks were prepared by a soft-templating and dip-coating method utilizing poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (Pluronic® F-127) as a structure-directing agent, resulting for the first-time in uniformly structured, crack-free, and optically transparent CuO thin films. The photoelectrochemical properties of the nanoporous CuO frameworks were investigated as a function of the calcination temperature and film thickness, revealing important information about the photocurrent, photostability, and photovoltage. Based on surface photovoltage spectroscopy (SPV), the films are p-type and generate up to 60 mV photovoltage at 2.0 eV (0.050 mW cm-2) irradiation for the film annealed at 750 °C. For these high annealing temperatures, the nanocrystalline domains in the thin film structure are more developed, resulting in improved electronic quality. In aqueous electrolytes with or without methyl viologen (as a fast electron acceptor), CuO films show cathodic photocurrents of up to -2.4 mA cm-2 at 0.32 V vs. RHE (air mass (AM) 1.5). However, the photocurrents were found to be entirely due to photocorrosion of the films and decay to near zero over the course of 20 min under AM 1.5 illumination. These fundamental results on the structural and morphological development upon calcination provide a direction and show the necessity for further (surface) treatment of sol-gel derived CuO photocathodes for photoelectrochemical applications. The study demonstrates how to control the size of nanopores starting from mesopore formation at 400 °C to the evolution of macroporous frameworks at 750 °C.

Water‐splitting processes require advanced catalysts for the electrocatalytic hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). A facile and cost‐effective approach using single‐source precursors (SSPs) to prepare active and durable bifunctional electrocatalysts consisting of core–shell structured transition metal phosphide (TMPs) nanoparticles dispersed and immobilized in a highly defective N‐, P‐codoped carbon matrix. The bimetallic FeNi phosphide supported on N‐, P‐codoped carbon is synthesized through pyrolysis at 900 °C under an argon atmosphere (FeNiP@NPC‐900), displaying promising electrocatalytic performance for both HER and OER, with low overpotentials of 191 and 278 mV, respectively. Furthermore, FeNiP@NPC‐900 exhibits remarkable durability in both acidic and alkaline electrolytes. The excellent catalytic and long‐term performance is attributed to several factors, including the novel SSP approach, which prevents the agglomeration of active TMPs particles, the in situ formation of exposed nanopores during the carbonization of the precursor without using surfactants, and the heterostructure between highly defective carbon and TMPs, which positively influences the electronic structure at the interface and facilitates charge transfer. The unique core–shell nanostructure protects the catalytically active phase from corrosion and synergistically promotes the activity performance. Therefore, a new strategy for designing active and stable heterostructured TMPs@carbon‐based electrocatalysts is provided. [ABSTRACT FROM AUTHOR]

In the present work, bulk Si3N4/HfBxN1‐x ceramic nanocomposites were successfully fabricated via a polymer‐derived ceramic approach. The chemical reaction to form the single‐source precursor was confirmed by FT‐IR and XPS, in which both Si−H and N−H groups of perhydropolysilazane react with borane dimethyl sulfide complex and tetrakis(dimethylamido) hafnium(IV). The investigation of the polymer‐to‐ceramic transformation of the synthesized precursors indicates that Hf‐ and B‐modified PHPS exhibits high ceramic yields of up to 100 wt % after pyrolysis at 1000 °C under ammonia. Moreover, XRD and TEM results show that the SiHfBN ceramics with a molar ratio of B : Hf=5 and 10 resist crystallization at temperatures up to 1500 °C and separate after annealing at 1700 °C into nanocomposites comprising of an α‐Si3N4 matrix with embedded ternary HfBxN1‐x phases, solid solutions of rock salt‐type HfN and HfB. Based on the investigation, warm‐pressing was applied to fabricate bulk SiHfBN specimens, and the oxidation behavior of samples annealed at 1700 °C was recorded at 1500 °C over a range of oxidation times between 1 and 50 h. The weight changes of Si3N4/HfBxN1‐x ceramics with B : Hf molar ratios of 2 : 1, 5 : 1 and 10 : 1 are 4.31 %, 4.37 % and 2.57 %, respectively. The formation of HfSiO4, B2O3 and SiO2 during oxidation plays a crucial role for the improvement of the oxidation resistance of the Si3N4/HfBxN1‐x ceramics. [ABSTRACT FROM AUTHOR]