STOPEC project

Development of Scalable Photo-chargeable Tungsten oxide/Tungstate Hetero-junction Photoanodes with Reversible Electron Storage for Solar Water Splitting Even at Night

A durable and efficient approach towards United Nations’ Sustainable Development Goals of Affordable & Clean Energy and Climate Action.

The rising global energy demand and rapid global warming induced by greenhouse gas emission from fossil fuels has made it urgent to shift to clean and renewable energy alternatives like solar energy. But sunlight is periodic, discontinuous and cannot be stored and transported directly. However, hydrogen fuel is highly energy-dense, storable, portable and has clean combustion by-products. Photoelectrochemical water splitting employs low band gap semiconductors that can absorb and effectively utilize solar energy to decrease the external voltage requirement of water electrocatalysis to get hydrogen fuel. Large research attention is on optimisation of the electrode material for water oxidation (at anode) due to the slow electron kinetics of this process, thereby determining the overall efficiency.

In this project, we choose the visible light active semiconductor WO3 as the primary photo-absorber due to its stability in acidic media, tuneable band gap, relatively long hole diffusion length (~150 nm) and favourable location of valence band maximum w.r.t water oxidation potential. Moreover, WO3 shows the property of photo-charging and reversible electron storage (simultaneous with photo-electrocatalysis) in presence of suitable electrolyte for possible round-the-clock H2 production, uninterrupted even at night. We aim to first address the drawbacks of WO3 like photo-corrosion, low absorption coefficient, etc. by forming heterojunction with semiconductor co-catalyst. The photoelectrochemical performance evaluation will be done using voltammetry, amperometry and impedance spectroscopy in a three-electrode system.  The investigation of continuous H2 production in the WO3 based PEC cells under illumination and then in dark, due to discharge of photocharged electrons shall be done by quantification of amount of hydrogen and oxygen produced.
The anodic oxidation method will be used for WO3 growth. It is dependent on voltage, time, electrolyte composition, etc., and will be optimized so that the surface morphology, pore size and thickness are suitable for overlayer deposition. Well dispersed Fe/Sn tungstate overlayer will be grown on WO3 by changing controllable parameters of wet impregnation/hydrothermal methods to select those resulting in enhanced performance compared to bare WO3. Performance of unbiased cell fabricated using suitable photocathode with the optimised photoanodes shall be investigated. 
Significance and Novelty
  • Novel combination of WO3 with 2 earth abundant metal tungstates (Fe and Sn), for lattice matching and light absorption; only theoretically predicted for PEC.
  • Porous WO3 by anodic oxidation of W: scalable, reproducible, offer better charge collection.
  • Reduce recombination of photo-excited e-h pairs by p-n junction type II band aligned heterostructures (less explored in anodized WO3): p-FeWO4/n-WO3 and p-SnWO4/n-WO3.
  • Electrocatalytic and protective co-catalyst overlayer on WO3 for longer operational stability.
  • Known reversible photoelectron storage effect in pristine anodic WO3 to be studied in heterojunction photoelectrodes; unexplored in WO3 / tungstate for ‘on-demand’ charge release in dark for H2 generation.
  • Obtain phase pure porous WO3 of micron range thickness.
  • p-type Fe/Sn tungstate overlayer growth on WO3 for band aligned heterojunction photoanodes.
  • Photocurrent ~2 times higher than pristine WO3 with onset at low bias (<0.5V vs RHE) with simultaneous photoelectron storage.
  • 3 hours of continuous stable photocurrent / H2 generation under light (>100 µmol-cm-2hr-1 H2 at near onset bias)
  • Night time H2 generation after photocharging (at ~1 order of magnitude lower).
  • Construct unbiased dual PEC cell with suitable reported photocathodes.
Added applicability of photoanodes: 
  • In photo-battery, photo-supercapacitor, PEC upcycling of organic waste to high value compounds, self-powered PEC sensing and disinfection. 
This research is part of the project No. 2022/47/P/ST5/00813 co-funded by the National Science Center and the European Union Framework Program for Research and Innovation Horizon 2020 under the Marie Skłodowska-Curie grant agreement no. 945339.
Principal Investigator: Dr. Piyali Chatterjee
Project location
Faculty of Chemistry, Department of Physical Chemistry and Electrochemistry, Jagiellonian University
Gronostajowa 2, Krakow 30-387, Poland (faculty website) (group website) 
Project news
Start: 01.10.2023, End: 30.09.2025
The scholarship holders working in the project will be students:
  1. Daniel Piecha
  2. Sebastian Kotarba 
Contact details
Principal Investigator's contact details:
Piyali Chatterjee, PhD
Jagiellonian University, 
Department of Physical Chemistry and Electrochemistry
Gronostajowa 2, Krakow 30–387, Poland
Phone: +48 510490888 
Project Supervisor/mentor's contact details:
Prof. Dr. hab. Grzegorz Sulka
Jagiellonian University
Department of Physical Chemistry and Electrochemistry
Gronostajowa 2, 30–387 Krakow, Poland
Phone: +48 12 686 25 18