Produção de hidrogênio via eletrólise da água utilizando PdNi NPs suportadas em carvões vegetais

The great exploration of the vegetable resources by the agro-industries leads to the formation of a huge quantity of waste. The resignification of these wastesis of extremely ambiental importance. To aggregate a residue into a technology and this way forming a product more noble product is the greatest motivation of thisresearch. Hydrogen is an energy vector of great aggregate value due to a big importance in the energy sector. The H2 synthesis by water electrolysis is a scientificand technological challenge, mainly to the catalytic point of view. This work will explore the use of PdNi NPs supported in vegetable charcoals from agro-industrial wastes as catalysts in the H2 production by water electrolysis. The residues used are: Corn (Zea mays) husk, Pequi (Caryocar brasiliense), Pinhão (Araucaria angustifolia) and Timbaúva (Enterolobium contortisiliquum). These were dried separately in a stove for 24 h at 105 ºC. After cooling to 25 oC, 7 g of dried waste was put in a muffle oven at 300 oC for 20 min. The products were charcoals which were used as catalytic support. The catalysts (PdNi NPs supported by Corn, Pequi, Pinhão and Timbaúva charcoals and Vulcan XC-72R carbon) were synthesized using NaBH4 [1]. These were characterized by X-ray diffraction, presenting face-centred cubic (fcc) structures characteristic of Pd metal and the charcoal (002) support peak appear at 2θ=25°.The electrodes were made by brushing technique with 0.5 mgmetal cm-2. The H2 production by water electrolysis in aqueous media of 3-triethylammonium-propanesulfonic acid tetrafluoroborate (TEA-PS.BF4) ionic liquid was evaluated using a chronoamperometry at -2 V vs. QRE-Pt (1800 s). The synthesized catalysts produced a H2 volume of 348, 180, 282, 72, 83 L g Pd-1 referred to PdNi catalyst supported in Corn, Pequi, Pinhão, Timbaúva coals and Vulcan XC-72R, respectively. The reaction mechanism of hydrogen production was evaluated by Tafel analysis (η = a + b log j, where b (V dec-1) is the Tafel coefficient, which indicates the rate of change of the current density, j (mA cm-2), with the applied overpotential,  (V). The b values were near to 40 mV dec-1, characteristic of the Volmer-Heyrovsky mechanism [2]. The Corn catalytic support presented bigger values of effective exchange current density, what reflects in a lower activation energy and, consequently, the greater produced volume of hydrogen.