Considering their superior charge-transfer characteristics, easy tenability of energy levels, and low production cost, organic semiconductors are ideal for photoelectrochemical (PEC) hydrogen production. However, organic-semiconductor-based photoelectrodes have not been extensively explored for PEC water-splitting because of their low stability in water. Herein, we report high-performance and stable organic-semiconductors photoanodes consisting of p-type polymers and n-type non-fullerene materials, which is passivated using nickel foils, GaIn eutectic, and layered double hydroxides as model materials. We achieve a photocurrent density of 15.1 mA cm−2 at 1.23 V vs. reversible hydrogen electrode (RHE) with an onset potential of 0.55 V vs. RHE and a record high half-cell solar-to-hydrogen conversion efficiency of 4.33% under AM 1.5 G solar simulated light. After conducting the stability test at 1.3 V vs. RHE for 10 h, 90% of the initial photocurrent density are retained, whereas the photoactive layer without passivation lost its activity within a few minutes.

A B S T R A C TLead-free perovskite oxide thin films prepared by alloying of titanates and materials with lower melting points are shown to have enhanced ferroelectric and dielectric properties. BaTiO 3 (or SrTiO 3 ) with 25% addition of BiFeO 3 has much improved crystalline perfection because of the lower melting point of the BiFeO 3 giving enhanced growth kinetics. The maximum dielectric peak temperature of BaTiO 3 is increased by~200°C and leakage currents are reduced by up to a factor of~100. The loss tangent reduces up to 300°C, with a factor of > 14 reduction at room temperature. The dielectric breakdown strength is higher by a factor of~3 (> 2200 kV cm ) and from room temperature up to 500°C the dielectric constant is > 1000. Also, a low variation of dielectric constant of~9% from room temperature to 330°C is obtained, compared to~110% for BaTiO 3 . The maximum polarization (P max ) is double that of BaTiO 3 , at 125.3 μC cm −2. The film has high energy storage densities of > 52 J cm −3 at 2050 kV cm −1 , matching Pb-based ferroelectric films. The strongly improved performance is important for applications in energy storage and in high temperature (up to 300°C) capacitors as well as wider application in other electronic and energy technologies.

The importance of hydrogen peroxide (H 2 O 2 ) continues to grow globally. Deriving the oxygen reduction reaction (ORR) toward the 2epathway to form H 2 O 2 is crucial for high H 2 O 2 productivity. However, most selective electrocatalysts following the 2epathway comprise carbon-containing organic materials with intrinsically low stability, thereby limiting their commercial applicability. Herein, layered double hydroxides (LDHs) are used as inorganic matrices for the first time. The LDH catalyst developed herein exhibits near-100% 2e -ORR selectivity and stably produces H 2 O 2 with a concentration of ≈108.2 mm cm -2 photoanode in 24 h in a two-compartment system (with a photoanode) with a solar-to-chemical conversion efficiency of ≈3.24%, the highest among all reported systems. Density functional theory calculations show that 2e -ORR selectivity is promoted by atomically dispersed cobalt atoms in (012) planes of the LDH catalyst, while a free energy gap between the * O and OOHstates is an important factor.

Photoelectrochemical overall water splitting without an external bias is demonstrated using an all-bismuth-based oxide tandem cell with a CuBi 2 O 4 photocathode and a BiVO 4 photoanode. A solution-based nitrate salt decomposition method is developed for preparing a crystalline p-type CuBi 2 O 4 film with a suitable band gap and Fermi level to serve as a photocathode for water splitting. The optimum CuBi 2 O 4 photocathode is prepared by three-layer deposition and heat-treatment at 823 K, which yields the highest photocurrent density of −0.66 mA cm −2 at 0.4 V RHE and reduction onset potential of ≥1.0 V RHE under 1 sun in O 2 -purged KPi electrolyte. The all-bismuth based oxide tandem cell of Pt/CuBi 2 O 4 photocathode and a cobalt-phosphate (Co-Pi) modified Mo-doped BiVO 4 photoanode give a photocurrent density of ∼0.15 mA cm −2 without any applied bias.

Highly porous thin films and nanostructure arrays are created by a simple process of selective dissolution of a water‐soluble material, Sr3Al2O6. Heteroepitaxial nanocomposite films with self‐separated phases of a target material and Sr3Al2O6 are first prepared by physical vapor deposition. NiO, ZnO, and Ni1− xMgxO are used as the target materials. Only the Sr3Al2O6 phase in each nanocomposite film is selectively dissolved by dipping the film in water for 30 s at room temperature. This gentle and fast method minimizes damage to the remaining target materials and side reactions that can generate impurity phases. The morphologies and dimensions of the pores and nanostructures are controlled by the relative wettability of the separated phases on the growth substrates. The supercapacitor properties of the porous NiO films are enhanced compared to plain NiO films. The method can also be used to prepare porous films or nanostructure arrays of other oxides, metals, chalcogenides, and nitrides, as well as films or nanostructures with single‐crystalline, polycrystalline, or amorphous nature.