Formic acid photoelectroreforming on bismuth vanadate based catalysts

Abstract

Hydrogen storage materials are a key factor in implementation of a sustainable hydrogen economy.1 Among many options, liquid organic hydrogen storage (LOHC) materials are of high interest due to their easy handling and implementation to existing infrastructure. A possible candidate for LOHC is formic acid (FA), a low toxicity, water miscible compound that can also be found in nature.2 Furthermore, a key advantage is the possibility of implementing a carbon neutral cycle by coupling carbon dioxide (CO2) reduction to FA with selective FA oxidation to CO2.3For the oxidative part of aforementioned cycle, most research up to now has focused on FA photoreforming over titanium dioxide (TiO2)4-7, a UV absorbing semiconductor, but little effort has been made to implement a semiconductor with absorption in the visible light range, such as bismuth vanadate (BiVO4), which recently has gained attention due to its capabilities for oxygen evolution reaction.8-10 This thesis focuses on utilisation of BiVO4 as a photocatalyst under applied external potential.Preliminary experiments were conducted in search of metal co-catalysts for support of the photocatalytic reaction on TiO2. The same metal co-catalysts were then introduced to BiVO4 based samples for use under photoelectrocatalytic conditions.It was found, that both copper (Cu) and (Ni) were suitable for selective photoreforming of FA to CO2 over TiO2 under UV illumination (365 nm). Furthermore, BiVO4 showed to be a selective catalyst for the oxidation of FA to CO2 under photocatalytic conditions (solar spectrum) with applied external potential of 0.4 V vs. reversible hydrogen electrode (RHE). It was then examined if Cu and Ni were also applicable as co-catalysts on BiVO4 under photoelectrochemical conditions. While addition of Copper co-catalyst to BiVO4 lead to unstable material, introduction of Ni as a co-catalyst was successful, showing promising results for the reduction of required energy for photoelectrochemical oxidation of FA over BiVO4.