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The exploration of promising renewable energy sources for the future is likely the most significant challenge for humanity. Hydrogen is considered to play a major role in the urgently required reorganization of our current energy sector. Water can be split into hydrogen and oxygen and therefore presents an in principle inexhaustible and environmentally friendly hydrogen source. However, electrochemical approaches for the cleavage of H2O remain challenging, especially considering that the experimentally required potential at which oxygen evolves is substantially higher than the theoretically required potential. This results in significant overpotentials (η) on the anode side, which limits the widespread applicability of this technique. Here, we have applied a two-step activation procedure of a Co-containing steel, which led to a significant reduction of η for the oxygen evolution reaction (OER) down to almost zero. The enhanced electrochemical behavior comes as a result of Li-ion doping, which leads to Li intercalation into the Co3O4 containing surface layer of the steel-ceramic composite material. Thus, our results indicate that additional metal doping and resulting surface modification is a promising strategy for achieving substantial OER at pH-neutral conditions close to the thermodynamic limit.
The use of proton exchange membrane (PEM) electrolyzers is the method of choice for the conversion of solar energy when frequently occurring changes of the current load are an issue. However, this technique requires electrolytes with low pH. All oxygen evolving electrodes working durably and actively in acids contain IrOx. Due to their scarcity and high acquisition costs, noble elements like Pt, Ru and Ir need to be replaced by earth abundant elements. We have evaluated a cobalt containing steel for use as an oxygen-forming electrode in H2SO4. We found that the dissolving of ingredients out of the steel electrode at oxidative potential in sulfuric acid, which is a well-known, serious issue, can be substantially reduced when the steel is electro-oxidized in LiOH prior to electrocatalysis. Under optimized synthesis conditions a cobalt-containing tool steel was rendered into a durable oxygen evolution reaction (OER) electrocatalyst (weight loss: 39 μg mm−2 after 50 000 s of chronopotentiometry at pH 1) that exhibits overpotentials down to 574 mV at 10 mA cm−2 current density at pH 1. Focused ion beam SEM (FIB-SEM) was successfully used to create a structure–stability relationship.
The photocatalytic activity of P25 TiO2 with 0.36 % (w/w) Pt co‐catalyst towards the formation of methane, in the presence of CO2 and H2O vapor, is investigated in a flow photoreactor under varying reaction conditions of temperature, water molar fraction in the dosed gas and residence time. Within the range of parameters studied, H2O molar fraction is found to be the most sensitive parameter, and its increase leads to larger production rates as well as to a significant slow down of photocatalytic activity loss. This observed activation with water content is in contrast to the effect known in neat P25 and it occurs in a regime of very large adsorbed H2O to CO2 excess, and can be understood in the context of hole extraction being much slower than electron extraction. These results also constrain the possible interpretation of the nature of the photocatalyst deactivation processes.
Weniger Gummiabfälle
(2020)
Enzymatic batch processes bear some disadvantages, such as the high quantity of enzyme, energy and labor needed and, consequently, high production costs. The aim of this study was the production of a sodium caseinate hydrolysate with improved antioxidative capacity and reduced bitterness in a continuous system to avoid such drawbacks. Therefore, a novel, food-grade, two-step enzymatic membrane bioreactor (EMBR) process was designed in which a functional improved permeate with a 33% increased antioxidativity compared to sodium caseinate was produced with the endopeptidases Sternzym BP 25201. This bitter permeate was subsequently debittered in a second EMBR step with commercial Flavourzyme, which was reduced in its endopeptidase activity. This resulted in a linear production of 7.5 gProduct h−1 of antioxidative (antioxidativity: +39% compared to sodium caseinate), debittered peptides. The influence of the peptidases on each other was excluded by separating the endo- and exopeptidases in two EMBR steps and a product with consistent properties like degree of hydrolysis, antioxidativity and taste was obtained. The process conditions chosen were optimal regarding a stable product formation for three days. Therefore, the process was superior in its productivity, enzyme usage and run time compared to an equivalent batch process.