Abstract:

Alcohols fuel electro-oxidation is significant to the development of direct alcohols fuel cells, that are considered as a promising power source for portable electronic devices. Currently, the catalyst was restricted by the serious poisoning effect and high cost of noble metals. Developing low-cost Pt alloy with high performance and anti-CO poisoning ability was highly desired. In this work, PtCo-NC catalyst was synthesized by combining Pt nanoparticles with ZIF-67 after annealing in the tube furnace and the in situ generated N-doped carbon from ZIF-67 was functionalized to support the PtCo alloy nanoparticle. The structure and morphology were probed by X-ray diffraction, scanning electron microscope and transmission electron microscope, and the electrochemical performance was evaluated for alcohols of methanol and ethanol oxidation in the acid electrolyte. Compared with the reference sample of Pt/C, several times performance enhancement for alcohols fuel oxidation was found on PtCo-NC catalyst as well as the good catalytic stability. Specifically, the peak current density of PtCo-NC was 79.61 mA∙cm⁻² for methanol oxidation, about 2.2 times higher than that of the Pt/C electrode (36.97 mA∙cm⁻²) and 2.5 times higher than that of the commercial Pt/C electrode (31.23 mA∙cm⁻²); it was 62.69 mA∙cm^–2 for ethanol oxidation, about 1.65 times higher than that of Pt/C catalyst (37.99 mA∙cm⁻²) and commercial Pt/C electrode (37.77 mA∙cm⁻²). These catalytic performances were also much higher than some analogous catalysts developed for alcohols fuel oxidation. A much higher anti-CO poisoning ability was demonstrated by the CO stripping voltammetry experiment, in which the CO_ad oxidation peak potential for PtCo-NC was 0.46 V, ca. 110 mV negative shift compared with Pt/C catalyst at 0.57 V. A strong electronic effect was indicated by the peak position shifting to the lower binding energy direction by 0.3 eV on PtCo-NC compared with Pt/C reference catalyst. According to the d-band center theory, the electron-enriched state of Pt will decrease the interaction strength of poisoning intermediates adsorbed on its surface; Moreover, according to the bifunctional catalytic mechanism, the presence of Co can form the adsorbed oxygen-containing species (―OH) more easily than Pt at low potentials, and this oxygen-species were helpful in the oxidation of CO_ad at neighboring Pt sites. The high catalytic performance for alcohols fuel oxidation could be due to the largely improved anti-CO poisoning ability and the synergistic effect between the in situ formed PtCo nanoparticles and the N-doped carbon support.

Key words: Alcohols oxidation reaction, Direct alcohol fuel cell, Electro catalyst, Pt-base catalyst, N-doped carbon