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17 Nov 2019
Explain it briefly?
Production from renewable sources Production of H_2 by electrolysis of water is costly and viable only in areas where electricity is cheap or if it is a byproduct of an eco-nomically important process. Environmental pressures are driving technologies to produce H_2 more efficiently from surplus or renewable energy, including solar and biological sources. Electrolysis is used to produce H_2 that is free from contaminants. To drive this reaction, a large overpotential is required to offset the sluggish electrode kinetics, particularly for the production of O_2. The best catalysts are based on platinum, but it is too expensive to justify its use in large-scale plants. As a consequence, electrolysis of water is economical and environmentally benign only if the electrical power stems from cheap, renewable resources or if it is surplus to demand. These conditions are found in countries that have plenty of hydroelectric or nuclear energy. There is also scope for off-shore wind farms that can employ resources far from the electricity grids and are far from the population areas that are otherwise necessary for conventional power generation. Electrolysis is carried out using hundreds of cells arranged in series, each operating at 2 V with iron or nickel electrodes and aqueous NaOH (or an ion-selective membrane) as electro- lyte (Fig. 10.5). Temperatures of 80-85 degree C are used to increase the electrolytic current and to lower the overpotential. The most important electrolytic H_2 production method is the chlor-alkah process (Box 1 1.2), in which H, is produced as a byproduct of NaOH manufacture. In this process the other gaseous product is Cl, which requires a lower overpotential than O_2. As yet, however, only about 0.1 per cent of the global H_2 demand is produced by electrolysis, including that produced in the chlor-alkali process. This percentage could be improved by the development of cheap and efficient clectrocatalysts to reduce the economically wasteful overpotential. Hydrogen can be produced by fermentation, using anaerobic bacteria that use cultivated biomass or biological waste as their energy source (Box 10.1). Research is also under way to establish how best to produce H_2 by exploiting solar energy directly either through physical methods (solar-powered thermolysis or photo)
Explain it briefly?
Production from renewable sources Production of H_2 by electrolysis of water is costly and viable only in areas where electricity is cheap or if it is a byproduct of an eco-nomically important process. Environmental pressures are driving technologies to produce H_2 more efficiently from surplus or renewable energy, including solar and biological sources. Electrolysis is used to produce H_2 that is free from contaminants. To drive this reaction, a large overpotential is required to offset the sluggish electrode kinetics, particularly for the production of O_2. The best catalysts are based on platinum, but it is too expensive to justify its use in large-scale plants. As a consequence, electrolysis of water is economical and environmentally benign only if the electrical power stems from cheap, renewable resources or if it is surplus to demand. These conditions are found in countries that have plenty of hydroelectric or nuclear energy. There is also scope for off-shore wind farms that can employ resources far from the electricity grids and are far from the population areas that are otherwise necessary for conventional power generation. Electrolysis is carried out using hundreds of cells arranged in series, each operating at 2 V with iron or nickel electrodes and aqueous NaOH (or an ion-selective membrane) as electro- lyte (Fig. 10.5). Temperatures of 80-85 degree C are used to increase the electrolytic current and to lower the overpotential. The most important electrolytic H_2 production method is the chlor-alkah process (Box 1 1.2), in which H, is produced as a byproduct of NaOH manufacture. In this process the other gaseous product is Cl, which requires a lower overpotential than O_2. As yet, however, only about 0.1 per cent of the global H_2 demand is produced by electrolysis, including that produced in the chlor-alkali process. This percentage could be improved by the development of cheap and efficient clectrocatalysts to reduce the economically wasteful overpotential. Hydrogen can be produced by fermentation, using anaerobic bacteria that use cultivated biomass or biological waste as their energy source (Box 10.1). Research is also under way to establish how best to produce H_2 by exploiting solar energy directly either through physical methods (solar-powered thermolysis or photo)
Tod ThielLv2
25 Jan 2019