| Utilizing solar energy to meet the energy demands of the world is a promising approach towards transitioning from fossil fuels dependency.Not only is solar energy a renewable energy source but also environmentally friendly and of much abundance.Photoelectrochemical water splitting is one of the promising ways of utilizing solar energy to split the water molecule to its component molecules H2 and O2.The resulting chemical fuel hydrogen(H2)can be used to satisfy energy needs and power economies as it has a high combustion energy and can be easily stored or transported.One of the materials being studied heavily for its application in water splitting is hematite(α-Fe2O3).Hematite is a low-cost semiconductor with a suitable bandgap of about 2.2 eV and is a promising material for future mass production of H2 at large economies of scale when its shortcomings are addressed.It suffers from slow oxygen evolution reaction(OER)kinetics and poor charge transport.To improve its water splitting performance,different cocatalyst materials are loaded onto it to help it achieve greater efficiencies.In this thesis,we used earth abundant cocatalyst materials(nickel,cobalt and aluminium)to decorate the hematite photoanode to improve its stability and enhance charge transfer for an overall better photoelectrochemical system.Chapter 1 introduces the challenges that brought about the development of photoelectrochemical(PEC)water splitting,the favorable materials for PEC water splitting and general introduction to OER cocatalysts used in tandem with PEC semiconductors to enhance their performance towards water splitting.The different technologies employed to capture and utilize solar energy are explored so as to give insights to the research choice endeavors.The inspiration drawn from the natural phenomena like natural photosynthesis to the current artificial photosynthesis development technology is highlighted and contrasted.In chapter 2,the loading of NiFeCoAlOOH nanoparticles onto titanium doped nanoporous hematite photoanode is discussed.Herein for the first time,we report the decoration of NiFeCoAlOOH nanoparticles on Ti-doped nanoporous hematite(Ti-PH)through a simple electroless ligand-controlled oxidation method.Due to the improved oxygen evolution reaction(OER)kinetics and reduced charge transfer resistance,the resulting Ti-PH/NiFeCoAlOOH photoanode exhibits excellent photocurrent density of 2.46 mA/cm2 at 1.23V vs.RHE and exceptionally great stability compared to Ti-PH or bare hematite(H).In addition,the photocurrent onset potential cathodically shifted by～60 mV compared to Ti-doped nanoporous hematite under AM 1.5G illumination(100 mW/cm2).The synthesis regimen for all the materials is presented with experimentation on the different loading amounts of cocatalyst materials that renders the best results being presented.X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),Scanning electron microscopy(SEM),Transmission electron microscopy(TEM),high-resolution transmission microscopy(HRTEM)and energy-dispersive X-ray microscopy(EDX)were utilized to characterize the photoanode system and the results are presented showing the NiFeCoAlOOH nanoparticles were successfully decorated onto the Ti-PH nanorods.The electrochemical methods have been outlined with results such as the outstanding stability for over 6 hours being presented.Utilizing UV-vis diffuse reflectance absorption spectra,we are able to deduce the slight improvement to the bandgap of the overall system which led to the enhancement of the photoelectrochemical performance.The impressive applied bias photon-to-current efficiency(ABPE)results and incident photon-to-current conversion efficiency(IPCE)results are presented to further support the improvement brought by the decoration of the NiFeCoAlOOH nanoparticles onto the Ti-PH nanorods.We believe this work offers a promising method for designing high-performance,stable and inexpensive catalysts of different morphologies for photoelectrochemical applications.Finally,after successful development of noble metal free photoelectrochemical system utilizing the earth abundant metals for cocatalyst material the future outlook of the technology is presented. |
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