Promoting nickel oxidation state transitions in single-layer NiFeB hydroxide nanosheets for efficient oxygen evolution.

Promoting the formation of high-oxidation-state transition metal species in a hydroxide catalyst may improve its catalytic activity in the oxygen evolution reaction, which remains difficult to achieve with current synthetic strategies. Herein, we present a synthesis of single-layer NiFeB hydroxide nanosheets and demonstrate the efficacy of electron-deficient boron in promoting the formation of high-oxidation-state Ni for improved oxygen evolution activity. Raman spectroscopy, X-ray absorption spectroscopy, and electrochemical analyses show that incorporation of B into a NiFe hydroxide causes a cathodic shift of the Ni2+(OH)2 → Ni3+δOOH transition potential. Density functional theory calculations suggest an elevated oxidation state for Ni and decreased energy barriers for the reaction with the NiFeB hydroxide catalyst. Consequently, a current density of 100 mA cm-2 was achieved in 1 M KOH at an overpotential of 252 mV, placing it among the best Ni-based catalysts for this reaction. This work opens new opportunities in electronic engineering of metal hydroxides (or oxides) for efficient oxygen evolution in water-splitting applications.

A Driving Method for Reducing Oil Film Splitting in Electrowetting Displays.

Electrowetting displays (EWDs) are one of the most potential electronic papers. However, they have the problem of oil film splitting, which could lead to a low aperture ratio of EWDs. In this paper, a driving waveform was proposed to reduce oil film splitting. The driving waveform was composed of a rising stage and a driving stage. First, the rupture voltage of oil film was analyzed by testing the voltage characteristic curve of EWDs. Then, a quadratic function waveform with an initial voltage was applied at the rising stage to suppress oil film splitting. Finally, a square wave was applied at the driving stage to maintain the aperture ratio of EWDs. The experimental results show that the luminance was increased by 8.78% and the aperture ratio was increased by 4.47% compared with an exponential function driving waveform.

Iron-cobalt bimetal oxide nanorods as efficient and robust water oxidation catalysts.

Cobalt-based oxides are considered as potential water oxidation catalysts for future artificial photosynthetic systems because of their high abundance, strong stability and efficient performance. Herein, a series of cobalt-based oxides, MnCo3-nO4 (M = Mn, Fe, Co) samples, were synthesized through changing the metal sources by a low-temperature coprecipitation method. These catalysts were investigated under photochemical and electrochemical water oxidation conditions. And they all exhibited efficient activity for water oxidation under alkaline, acidic and neutral conditions under visible light irradiation. An excellent O2 yield of 90.4% for Fe-Co bimetal oxide (Fe1.1Co1.9O4) nanorods was obtained under optimal conditions (photoirradiation at λ ≥ 420 nm, [Ru(bpy)3](ClO4)2 as the photosensitizer, Na2S2O8 as the oxidant in borate buffer at pH = 9.0, bpy = 2,2-bipyridine). Among MnCo3-nO4 samples, Fe1.1Co1.9O4 nanorods were proved to be the optimal electrocatalytic water oxidation catalyst as well. Multiple experiments (SEM, FT-IR, XRD, XPS, Bulk electrolysis) were used to test the stability of Fe1.1CO1.9O4 and these results indicate that Fe1.1CO1.9O4 nanorods are highly stable. Furthermore, based on Mott-Schottky and cyclic voltammetry analysis, the best balanced flat-band potential of Fe1.1CO1.9O4 nanorods is just located at the middle position between the oxidation potential of O2/H2O and the half-wave potential of [Ru(bpy)3]3+/2+, which was probably responsible for their superior photocatalytic water oxidation performance.