DESENVOLVIMENTO DE CATALISADORES PARA AS REAÇÕES DE REDUÇÃO E DESPRENDIMENTO DE OXIGÊNIO USANDO COMBINAÇÕES DE ÓXIDOS DE COBALTO, NÍQUEL E PLATINA SUPORTADOS OU NÃO EM NANOFITAS DE GRAFENO

Abstract

In order to attend the society energy needs there is a continuum effort in the search for clean, efficient and sustainable energy generation. Among several existing technologies, fuel cells and electrolyzers play a fundamental role, but depend on the efficient catalysis of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Pt, Ru and Ir–based catalysts are normally used in these devices, although they present disadvantages like high–cost and scarcity. Therefor a huge effort has been devoted to the search for low–cost, efficient and robust catalysts for ORR and OER, and in order to replace noble metals or to reduce their use, transition metals have shown a promising performance in the catalysis of both reactions. This work sought to develop efficient ORR and OER catalysts based on Co, Ni and Pt combinations whether supported or not in graphene nanoribbons (GNRs). CoNi/GNR and PtCoNi/GNR nanocomposites as well as NiCo2O4 nanoparticles exhibited uniform distribution of metals on the surface and stability in strongly alkaline solutions. Among the investigated electrocatalysts, PtCoNi/GNR was the best and the most stable ORR catalyst, with low peroxide production mainly following the 4 electrons pathway. The presence of Pt0 and Pt2+ species supported in the CoNi/GNR nanocomposite, the synergistic effects between Pt and the Co2+, Co3+, Ni2+, Ni3+ ions as well as the metal/support interactions promoted an improvement in the catalytic properties of the catalyst. The modified electrode PtCoNi/GNR’ was produced with low content of Pt (22.5 μg cm–2) and displayed a behavior comparable to Pt(20%)/C. On the other hand, NiCo2O4 was found to be the best and most stable OER catalyst. Its nanoparticles of approximately 20 nm, with Co2+, Co3+, Ni2+ e Ni3+ ions intercalated across the nanostructures as well as the synergistic effects between the species were responsible for suitable electrocatalytic properties, with major OH– production at the end of the reaction. Besides, the use of different support electrodes revealed the intrinsic activity of NiCo2O4, resulting in OER faradaic efficiency close to 80% when the Au electrode was used as support to NiCo2O4.