Hydrogen Production from Water (via Photoelectrochemical Water Splitting) and Biomass Derivatives (via Aqueous Phase Reforming)

Hydrogen production from renewable sources such as water and biomass derivatives, is a promising and sustainable way of storing energy in the form of chemical fuel on a large-scale. In this regard, photoelectrochemical (PEC) water splitting has been found to be a potential approach and therefore, has been extensively studied in recent years. The desired efficiency of > 10% (STH) has already been achieved in laboratory scale. However, the stability of most of the suitable semiconductors (absorber layer in photoelectrodes) is a major issue due to the existence of corrosion potentials within the bandgap.
 
This talk presents the development of stable photocathode (for H₂ evolution) and photoanode (for O₂ evolution) devices based on Cu₂O and CdS as the light absorber respectively. Inherent in the above statement is the development of low-cost, efficient, and robust protective layers for the devices in both substrate (device on Au-coated glass) and superstrate (device on F-doped SnO₂, FTO-coated glass) configurations. Photoinduced conducting atomic force microscopy (c-AFM) reveals shunts and sub-bandgap states at the grain boundaries of the electrodeposited Cu₂O. To minimize shunting, we developed a method to obtain larger grains of Cu₂O via electrodeposition (two-step deposition) method. The Cu₂O photocathodes were protected with electron selective layers of ALD-TiO₂ (~ 10 nm) and CVD-Graphene, resulting in higher photocurrent (3 mA cm^-2), twice that of a bare Cu₂O electrode at 0.0 V vs RHE. The protected device shows a slow decay till 5-6 min and later, it generates stable photocurrent till 35 min of the experiment.
 
The photoanode was fabricated via a low-cost solution processing method in a core-shell structure for effective charge separation. The core, ZnO nanorods were optimized to grow sparsely such that the active absorber material, CdS can be loaded more in the interspace of the nanorods. A mesoporous (m-) NiO layer on top led to the mitigation of photocorrosion, acted as a cocatalyst to enhance the kinetics of oxygen evolution reaction, and provided a larger surface area at the electrode-electrolyte interface. The m-NiO coated photoanode resulted in a stable photocurrent of 2.15 mA cm^-2 at 1.23 V vs RHE.
 
Apart from the above projects, this talk also includes the synthesis of an active and stable catalyst for Aqueous Phase Reforming (APR) of diol and polyol for H₂ production in fixed-bed and batch reactors. Pt, Ru on Al₂O₃ and Ac-Carbon shows good activity. However, the metal nanoparticles agglomerate within a short period of time in the reaction condition, thereby slowing down the conversion rate. Use of m-Carbon as support may be a major focus of future study.