The electrochemical reduction of formic acid to methanol
Four anodic electrocatalytic powders were tested for water electrolysis. Of these a synthesised 70:30 mol% IrO2:TaC showed the best catalytic activity as it produced the highest current densities at both the stop potential of linear sweep voltammetry and the applied potential during chronoamperometric studies. The onset potential was very similar between all samples ranging between 1.49 and 1.50 V. Field emission scanning electron microscopy showed the emergence of a platy, vitreous-like phase in the synthesised powders with particle agglomerations with rounded edges, increasing the catalytic activity in comparison to commercial IrO2. For the reduction of formic acid to methanol experiments, the 70:30 mol% IrO2:TaC electrocatalyst was used as the anodic electrocatalyst and polyaniline (PANI) as the cathodic electrocatalyst. In eight samples collected from five of the nine membranes which were prepared, methanol was detected by liquid injection gas chromatography. The retention time of methanol varied between 4.62 and 4.97 minutes. This range is attributed to changes made in the gas chromatograph setup between tests. With the increase in applied potential, a higher current density and an increase in the concentration of methanol (%v/v) were observed in samples of the same membrane. The highest production of methanol was found in membrane B2 run at 5.1 V with a concentration of 0.1451 %v/v, this sample produced the highest current density in linear sweep voltammetry experiments, although it only produced the second highest current density for chronoamperometric experiments. This suggests that the catalytic activity for the reduction of formic acid to methanol is not necessarily dependent on the current density produced by the system.
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