Amorphous NiFeB nanoparticles realizing highly active and stable oxygen evolving reaction for water splitting

The development of highly efficient and inexpensive catalysts for oxygen evolving reactions （OERs） is extremely urgent for promoting the overall efficiency of water splitting. Herein we report the fabrication of a series of amorphous NiFeB nanoparticles with varying atomic ratios of Fe to （Ni ＋ Fe） （XFe） by a facile chemical-reduction method. The amorphous NiFeB （XFe=0.20） nanoparticles, combining the merits of in situ formation of borate-enriched NiFeOOH catalytic surface layers, intrinsic amorphous nanostructures, and an optimized degree of Fe doping, displayed highly active electrocatalytic performance towards the OER in a broad range of pH values （from alkaline to neutral conditions）. The catalyst exhibited a relatively low overpotential of 216 mV with a Tafel slope of 40 mWdec on Ni foam and 251 mV with a Tafel slope of 43 mV/dec on glassy carbon at 10 mA/cm2 in a 1 M KOH solution, demonstrating much greater OER efficiency than that of commercial RuO2. Long-term stability testing of the OER performance of NiFeB （XFe = 0.20） by chronoamperometry （overpotential （η） = 320 mV） over 200 h revealed no evidence of degradation. Facile, scalable synthesis and highly active water oxidation make the NiFeB nanoparticles very attractive for OER electrocatalysis.

Mesoporous nickel-iron binary oxide nanorods for efficient electrocatalytic water oxidation

The design and fabrication of low-cost, high-effidency, and stable oxygen-evolving catalysts are essential for promoting the overall efficiency of water electrolysis. In this study, mesoporous Ni1-xFexOy （0 〈 x 〈 1, 1 〈y 〈 1.5） nanorods were synthesized by the facile thermal decomposition of Ni-Fe-based coordination polymers. These polymers passed their nanorod-like morphology to oxides, which served as active catalysts for oxygen evolution reaction （OER）. Increasing the Fe-doping amount to 33 at.% decreased the particle size and charge-transfer resistance and increased the surface area, resulting in a reduced overpotential （-302 mV） at 10 mA/cm^2 and a reduced Tafel slope （-42 mV/dec）, which were accompanied by a far improved OER activity compared with those of commercial RuO2 and IrO2 electrocatalysts. At Fe-doping concentrations higher than 33 at.%, the trend of the electrocatalytic parameters started to reverse. The shift in the dopant concentration of Fe was further reflected in the structural transformation from a NiO （〈33 at.% Fe） rock-salt structure to a biphasic NiO/NiFe204 （33 at.% Fe） heterostructure, a NiFe204 （66 at.% Fe） spinel structure, and eventually to α-fe203 （100 at.% Fe）. The efficient water-oxidation activity is ascribed to the highly mesoporous one-dimensional nanostructure, large surface area, and optimal amounts of the dopant Fe. The merits of abundance in the Earth, scalable synthesis, and highly efficient electrocatalytic activity make mesoporous Ni-Fe binary oxides promising oxygen-evolving catalysts for water splitting.

Heat Denaturation of Protein Structures and Chlorophyll States in PSII Membranes

Heat denaturation is an important technique in the study of the structure and function of photosynthetic proteins. Heat denaturation of photosystem II (PSII) membrane was studied using circular dichroism (CD) spectroscopy, differential scanning calorimetry (DSC) and oxygen electrode. Complete loss of oxygen evolving activity of the PSII membrane was observed at temperatures below 45℃ . The decrease of excitonic interaction between chlorophyll molecules occurred more rapidly than the change of the protein secondary structure of the PSII membrane at temperatures above 45℃ . The results indicate that the protein secondary structure of the membrane proteins in PSII membranes is more stable than the excitonic interaction between chlorophyll molecules during heat denaturation.