Direct alcohol fuel cells formaldehyde

The main problems regarding the replacement of batteries by direct alcohol fuel cells are related to the largest volume required by the fuel cells, as compared to the batteries which have become highly compact (because DAFCs have not reached yet high efficiencies), elimination of residues of the methanol partial oxidation (generally mixtures of water with formic acid, methyl formate, and formaldehyde), and the high temperature which can reach the DAFC (up to around 85 °C for cells using Nafion membranes) [11, 12]. 

The conventional electrochemical reduction of carbon dioxide tends to give formic acid as the major product, which can be obtained with a 90% current efficiency using, for example, indium, tin, or mercury cathodes. Being able to convert CO2 initially to formates or formaldehyde is in itself significant. In our direct oxidation liquid feed fuel cell, varied oxygenates such as formaldehyde, formic acid and methyl formate, dimethoxymethane, trimethoxymethane, trioxane, and dimethyl carbonate are all useful fuels. At the same time, they can also be readily reduced further to methyl alcohol by varied chemical or enzymatic processes. 

Fuel cells using directly liquid fuels are advantageous in this aspect. Methanol, formaldehyde (water solution), formic acid (water solution) and hydrazine are among fuels relatively easy to oxidize electrochemically. Alcohol and hydrocarbon with larger molecular weight are much harder to oxidize completely to C02- Other qualifications to be considered are price, availability, safety, energy density and ease of handling. 

Here, M represents the electronically conducting electrode material (e.g.. Ft) that is not involved in the overall reaction and plays the role of an electrocatalyst for the reaction. The last intermediate step occurs in two identical consecutive steps since electron transfer occurs by quantum mechanical tunneling, which involves only one electron transfer at a time. When multistep reactions take place, there is the possibility of parallel-intermediate steps. The parallel-step reactions could lead to the same final product or to different products. Direct electro-oxidation of organic fuels, such as hydrocarbons or alcohols, in a fuel cell exhibits this behavior. For instance, in the case of methanol, a six-electron transfer, complete oxidation to carbon dioxide can occur consecutively in six or more consecutive steps. In addition, partially oxidized reaction products could arise, producing formaldehyde and formic acid in parallel reactions. These, in turn, could then be oxidized to methanol. 

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