Abstract:

Phosphomolybdic acid was investigated as a mediator for indirect carbon electrooxidation at low temperatures. Linear sweeping voltammetry and chronoamperometry experiments showed that the carbon electrooxidation process was influenced by the type of carbonaceous material, reaction conditions, reaction time, and phosphomolybdic acid concentration. The mechanism underlying indirect carbon electrooxidation was explored using cyclic voltammetry. The results showed that the reactivity of coconut-derived activated carbon was higher than that of coal-derived activated carbon or coal in the chemical reaction between phosphomolybdic acid and carbon materials. Sunlight and heating to 80℃ similarly improved the efficiency of the indirect carbon electrooxidation. The electrooxidation mechanism is as follows:Mo^VI in phosphomolybdic oxidizes carbon to form Mo^V, and is then electrooxidized back to Mo^VI in an anodic reaction, releasing the electron obtained from the carbon material. This process facilitated the indirect electrooxidation of carbon at low temperatures. Sunlight was found to enhance the rate of the chemical reaction between phosphomolybdic acid and carbon materials in two ways:1) thermally by increasing the reaction temperature and thus improving the reaction rate; 2) photocatalytically, as sunlight absorbed by phosphomolybdic acid is converted into chemical energy, which is the main effect. A full cell test with phosphomolybdic acid demonstrated a power density of 0.087 mW·cm^-2 at room temperature, indicating that the concept of low-temperature carbon fuel cells is feasible.

Key words: Low-temperature carbon fuel cell, Indirect electrooxidation, Phosphomolybdic acid, Activated carbon, Sunlight irradiation