In parallel with the above discussion concerning oxidation ,the main secondary reaction here is water version . The hydrogen thus produced can sometime be sold .Their are effort to utilize it in device such as fuel cell that work with higher efficiencies than the combustion engines .
The electrochemical reduction processes that have reached the highest degree of maturity are undoubtedly those for metal ion recovery from their dissolved ions , as discussed below . Other noxious compound amenable for direct reduction include: