On‐Line FTIR Spectroscopic Investigations of Methanol Oxidation in a Direct Methanol Fuel Cell

Abstract

A real-time Fourier transform infrared spectroscopy (FTIRS) analysis of the products of methanol oxidation in a prototype direct-methanol fuel cell operating at high temperatures (150 to 185°C) is reported here. The methanol oxidation products on platinum black and platinum-ruthenium catalyst surfaces were determined as a function of the fuel cell operating temperature, current density, and methanol/water mole ratio. Neither formaldehyde nor formic acid was detected in anode exhaust gas at all cell operating conditions. The product distributions of methanol oxidation obtained by on-line FTIRS are consistent with our previous results obtained by on-line mass spectroscopy under similar conditions. With pure methanol in anode feed, methanaldimethylacetal was found to be the main product, methyl formate and CO2 were also found. However, when water was present in the anode feed, the main product was C02, and the formation of methanaldimethylacetal and methyl formate decreased significantly with increase of the water/methanol mole ratio. Increase of cell operating temperature enhanced the formation of CO2 and decreased the formation of methanaldimethylacetal and methyl formate. Pt/Ru catalyst is more active for methanol oxidation and has a higher selectivity toward CO2 formation than Ptblack. Nearly complete methanol oxidation, i.e., the product was almost exclusively C02, was achieved using a Pt/Ru catalyst and a water/methanol mole ratio of 2 or higher in the anode feed at a temperature of 185°C or above.

Kinetics and Mechanism of the Electrooxidation of Formic Acid—Spectroelectrochemical Studies in a Flow Cell

“…This reaction can be considered as a model reaction for the electrooxidation of small organic molecules. In addition, it is also of technical interest, as formic acid is a reaction intermediate in direct methanol fuel cells [6] and was also proposed as a fuel for lowtemperature fuel cells. [7] It is generally accepted that the reaction proceeds through two different reaction pathways ("dual-path mechanism"): an "indirect" pathway involving formic acid dehydrogenation and subsequent electrooxidation of the resulting adsorbed CO to CO 2 , and a "direct" pathway, which proceeds directly, without CO ad formation, to CO 2 .…”

The influence of impurities in high temperature polymer electrolyte membrane fuel cells performance

“…For the MEA tested at 180 ºC, the value for the high frequencies resistance increased sharply during the three synthetic reformate cycles when compared to first three cycles MEAs 1-3. High temperature DMFC studies, based on a phosphoric acid PBI MEAs, showed that an increase in the operating temperature improves the kinetics of the methanol oxidation and induces a shift of electrochemical selectivity toward complete oxidation of methanol to CO 2 , reducing the formation of intermediates [3].…”

“…A high temperature DMFC was first studied in the 1990's using phosphoric acid doped PBI as electrolytes [3][4][5]. The assembled DMFC reached a maximum of 0.1 W·cm -2 , at 200 °C [4].…”

Estudo da eletrocatálise da reação de oxidação do glicerol sobre as fases intermetálicas ordenadas PtSn e AuSn

“…A banda em 1739 cm -1 se inicia em 0,70 V e pode ser atribuída ao estiramento da ligação C=O de um grupo carbonil proveniente de um aldeído (-CHO) e/ou de um ácido carboxílico (-COOH) (BRON e HOLZE, 2000;LIMA et al, 2003;VIGIER et al, 2004), já que é muito difícil especificar a procedência deste grupo, uma vez que a banda C=O para um grupo ácido e para um aldeído estão separadas por cerca de (CHANG et al, 1990;LI et al, 1997;SOUZA et al, 2002;LIMA et al, 2003 SMITH et al, 1999;XIA, 1999), uma vez que os átomos de Sn promovem um aumento na distância entre os sítios ativos de Pt, dificultando assim a adsorção de CO na configuração em ponte.…”

“…Desta forma, sugere-se que a produção de CO 2 não se deve apenas a oxidação de CO ads , podendo ocorrer também a partir da oxidação sucessiva dos intermediários reacionais oriundos da eletrooxidação do glicerol. , esta banda é detectável em torno de 1,20 V e corresponde a deformação assimétrica da molécula de CO 2 (CHANG et al, 1990;LI et al, 1997;SOUZA et al, 2002;LIMA et al, 2003). Em 1645 cm , que se forma a partir de 0,90 V no Au e 1,00 V no AuSn, indica a formação espécies intermediárias contendo grupamentos carbonil (C=O), provavelmente proveniente de aldeídos e/ou ácidos carboxílicos (BRON e HOLZE, 2000;LIMA et al, 2003;VIGIER et al, 2004).…”