Efeitos térmicos durante a foto-eletro-oxidação de glicerol catalisada por CdS

Abstract

Cadmium sulfide (CdS) is one of the most important chalcogenides applied to water splitting, which has a band gap of 2.4 eV that suits very well with the solar spectrum. Moreover, CdS possesses a strong reduction activity for H+ to H2, which makes this material interesting as a cocatalyst with another material for water splitting. Unfortunately, the use of water as electron source (oxygen evolution reaction) is difficulted due to the high overpotential and sluggish kinetic. Thereby organic molecules, as glycerol, oxidation appears as an alternative anodic reaction once it has high power density, renewability and low cost. In this work we focused on the glycerol electro-oxidation reaction (GEOR) catalyzed by FTO/CdS decorated with Platinum above or between FTO/CdS films under visible light irradiation and from 15 to 35°C temperature range. The CdS film was deposited by chemical bath deposition and Pt were deposited from Pt2+ precursor. The films were characterized by Raman and UV spectroscopy, XRD and SEM techniques. Electrochemical experiments were conducted in a quartz window 3 electrodes glass cell, with same solution reversible hydrogen electrode as potential reference and a platinum plate as counter electrode. The measurements were performed in KOH 0.1 mol L-1 and glycerol 1.0 mol L-1 under 100 mW cm-2 light irradiation. The experiments showed that increasing temperature the photocurrent also increases, following the Arrhenius equation and resulting in an apparent activation energy (Ea) of 35, 35 and 26 kJ mol-1 for the FTO/CdS, FTO/CdS/Pt and FTO/Pt/CdS, respectively, for potential under 0.5 V. For potential above 0.6 V the Ea decreases linearly with the potential increasing, tendency which is observed when Pt electrode is used as catalyst and probably linked with GEOR. The above results suggest that glycerol is a candidate to replace water in the anodic process for H2 production, and that increasing the temperature the kinetics of the process is improved.