Alka Pareek

Nanoniobia Modification of CdS Photoanode for an Efficient and Stable Photoelectrochemical Cell

Herein we report the surface modification of a CdS film by niobia nanoparticles via thioglycerol as an organic linker and thus fabricate an efficient and a stable photoanode for a photoelectrochemical (PEC) cell. We have synthesized three differenly sized (∼3, ∼6 ,and ∼9 nm) niobia nanoparticles by a hydrothermal synthesis approach and have further investigated the particle-size-dependent PEC performance of the nanoparticle-modified CdS photoanode. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) confirm the formation of Nb2O5 nanoparticles that are prepared via decomposition of the niobium peroxo complex during the hydrothermal reaction and reveal the presence of surface OH(-) groups over niobia nanoparticles that impart a high catalytic property to a material. The nano-Nb2O5-modified photoanode displayed a 23-fold higher power conversion efficiency compared to that of CdS. This modified structure increases the open circuit voltage (OCV) from 0.65 to 0.77 V, which is attributed to the nano-Nb2O5-induced surface passivation effect over bare CdS. Linking of nanoparticles on the CdS surface improves the photocorrosion stability of the CdS photoanode for even longer than 4 h in contrast to the tens of minutes for the base CdS surface. The uniform coverage of the CdS photoanode surface by niobia nanoparticles is thus found to be the controlling parameter for achieving a higher PEC performance and stability of the photoanode. This finding directed us to design an improved CdS photoanode for efficient and prolonged PEC hydrogen generation from a PEC cell.

Fabrication of a highly efficient and stable nano-modified photoanode for solar H2 generation

A highly efficient and stable CdS–TiO2 nano-modified photoanode (NMP) was achieved by a simple chemical linking method. Both efficiency and stability were enhanced by attaching thioglycerol linked TiO2 nanoparticles over CdS. The NMP generated twice the photocurrent than an as-made CdS photoanode and displayed a photoelectrochemical stability of minimum 9h of PEC testing.

Ultrathin MoS2–MoO3 nanosheets functionalized CdS photoanodes for effective charge transfer in photoelectrochemical (PEC) cells

The present study focuses on the synthesis of MoS2–MoO3 nanostructures via a hydrothermal method and their application in the modification of CdS photoanodes. Structural characterization reveals that with an increase in the hydrothermal reaction time the fraction of the MoS2 phase increases in the MoS2–MoO3 nanostructures, with MoS2 being dominant in the sample obtained at the maximum reaction time. TEM characterization reveals the formation of ultra thin nanosheets in the MoS2–MoO3 system. Correspondingly, the bandgaps estimated from the Tauc plot analysis indicate a bandgap tuning from 2.40 eV to 1.73 eV for these Mo-nanostructures. The surfaces of spray deposited nanostructured CdS thin films were further modified with these Mo-nanostructures via a very simple and economic chemical impregnation method. The CdS photoanodes modified with the MoS2–MoO3 nanosheets exhibit the highest PEC performance which is 4 times the photocurrent of bare CdS photoanodes. In addition, the stability of the modified photoanodes is enhanced to more than 8 hours compared to a few minutes for bare and photocorrosive CdS. The improved PEC performance is attributed to the formation of the n-CdS/p-MoS2 junction that suppresses the undesirable electron–hole recombination process and thus improves the charge transfer process. A solar-to-hydrogen conversion efficiency of 1.9% is reported for the MoS2–MoO3 nanosheets modified CdS photoanode.

Efficiency and stability aspects of CdS photoanode for solar hydrogen generation technology

Photoelectrochemical (PEC) cell based technology is expected to be one of the easiest green technologies to harness and to convert available solar energy into hydrogen [1]. Among the known systems of GaAs, Si, GaP and CdS- Cadmium sulphide is one of the best suited PEC materials that display a balance between its efficiency and stability. It has capability to absorb the visible light photons (E~1.5eV - 3eV), and displays the band- energetics that suits for water-splitting reaction (H2O→H2+O2), that ultimately is based on the electronic and optical structure of the sulphides. However, the photo-induced dissolution of CdS in an electrolyte during its photo-illumination in PEC cell is its major drawback [2]. Though arsenides and phosphides show higher efficiency however CdS exhibits significant stability. In contrast though TiO2/ ZnO show good stability but CdS displays good optical response towards visible light photons as compared null response of titanate like systems. This necessitates one to identify the practical way to inhibit the photocorrosion in case of CdS photoanodes which is mainly facilitated due to interaction of photogenerated holes with CdS lattice. In past, Pt/ RuO2/ Ru modified CdS surface were found to control the unwanted photocorrosion [3]. Commercially, usage of such materials is un-economic option for any technological usage. The present work discusses that with advent of present day new synthetic routes how the dynamics of photo generated holes and electrons can be controlled to improve the stability and efficiency of the sulphide photoanodes, which in turn shows an an improvement in the performance and stability of the PEC cell for desirable technological applications.