Tham khảo tài liệu 'sustainable energy harvesting technologies past present and future part 13', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Hydrogen from Stormy Oceans 229 2H2O 2e- H2 2OH- 5 The observed pH shifts are of course increasing with increasing current density and decreasing with increasing agitation of the seawater electrolyte. Already after the first modern energy crisis thirty years ago . Bockris Bockris 1989 in his book Energy Options has precisely specified the choice of electrode materials and electrochemical conditions to get efficient hydrogen generation from sea water. If the electrodes are properly selected and adjusted respectively then chlorine can largely be excluded. This can especially be achieved by choosing highly selective catalysts for oxygen evolution. When for example a manganese oxide containing material is used then oxygen evolution at high current densities can be achieved with oxygen evolution and less than chlorine evolution Izuma et al. 1998 . When manganese oxide was mixed with molybdenum oxide almost 100 oxygen evolution efficiency was obtained even at high current densities of 1000 A m2 Fujimura et al. 1999 . Such selective materials for oxygen evolution should be intensively studied to obtain optimal electrochemical behaviour for the generation of pure hydrogen. In this connection it is interesting to note that the microscopic and macroscopic algae in the oceans had to overcome exactly the same technical electrochemical problem with respect to chlorine evolution. They also aimed at liberating oxygen from sea water which involves a complex 4-electron extraction from water but had to suppress chlorine evolution which is a kinetically much simpler electrochemical process. Nature obviously succeeded since there is no chlorine evolution problem in the photosynthetic process. And it succeeded using a molecular CaMn4Ox catalysis complex which contains manganese as the above mentioned technical catalyst. Sea water also contains a series of ions of which Ca2 and Mg2 can produce problems at he hydrogen evolving cathode. Proton consumption there generates .
