The world is now diversifying its energy sources to meet the growing global fuel demand. Finding clean and sustainable sources of energy to reduce carbon emissions and protect the environment is one of the most important challenges that require further research work to develop promising technologies to solve this dilemma and open up new investment areas, and Saudi Arabia has natural potential to take advantage of the enormous opportunities in the renewable energy sector.
Hydrogen gas is a sustainable alternative to energy and is considered to be a clean fuel. Its combustion produces water vapor and is therefore environmentally friendly. In addition to being more efficient, the amount of energy produced by one kilogram of hydrogen fuel is equivalent to the energy produced by 2.8 kg Fossil fuels, and hydrogen as an important feedstock for petrochemical reactions and processed fertilizers.
Recently, a research team at KFUPM led by Dr. Uhsan Qurashi, a researcher at the Center for Excellence in Research for Nanotechnology , has developed Nanomaterials and semiconductors for the production of hydrogen in a process called "artificial photosynthesis" which makes use of solar energy, taking advantage of the Kingdom's distinctive location on the solar belt, which receives direct natural radiation of more than 6000 watts per hour / A research paper with a high impact factor (15.5) was published among the highest impact factors for a research paper published by the university in recent years.
Artificial photosynthesis is a chemical process that mimics natural photosynthesis to convert sunlight, carbon dioxide, water into various value added products such as carbohydrates, oxygen and hydrogen by storing energy from sunlight in the form of chemical bonds (solar fuels. Hydrogen is a clean fuel and an important feedstock in petrochemical reactions and fertilizers produced by various methods such as steam methane reforming (SMR), electrolysis, biological processes, solar thermal and more recently artificial photosynthesis. Hydrogen produced by SMR releases 240 mega tones CO2 yearly and conventional electrolysis is limited by usage of precious metals (platinum and iridium oxide).
Photo-electrochemical (PEC) water splitting is carried out in photo-electrochemical cells when solar light is used as energy source for electrolysis of water to produce hydrogen as clean fuel using semiconductor as photo-anode and cathode desirably under neutral pH. Essentially in photo-electrochemical cells, there are couple of possible configurations such as n-type semiconductor as photo-anode with metal cathode, photo-anode and photocathode, photocathode with metal anode. An example of photo-electrochemical cell is demonstrated in the figure 1 where semiconductor is shown as photo-anode and platinum as cathode. There are different enthralling challenges in solar hydrogen production such as complex energy intensive oxygen evolution reaction (OER) which involves four electron transfer, swift recombination, minimal visible light absorption, relatively low stability, cost and geometries of photo-electrochemical cells etc,. These are mostly fundamentals aspects related to the nature of electrode materials and photoelectrosynthetic cell design.
Dr. Ahsanulhaq Qurashi and his research team is presently working on development of high performance earth abundant semiconductor materials predominantly pursuing photo-electrochemical OER reactions.
Recently they developed sonochemically GaON nanosheets without using ammonia as nitrogen source. For the synthesis of GaON nanosheets, initially high purity gallium metal reacted with ethylene amine sonochemically followed by solvothermal treatment in 180°C to produce high yield gallium-amine precipitate (Ga-ethylenediamine complex). Later black precipitate was dried and treated at 500°C for 4 hours to produce GaON nanosheets and confirmed the presence of nitrogen by XPS. GaON sheets were introduced in-situ to make GaON/ZnO on FTO glass substrate in a single step. Finally this GaON/ZnO photoanode was evaluated and showed overall water splitting with OER dominated reactions (video). Also, DFT calculations were carried to correlate experimental findings. These results were published in Nano Energy (Nano Energy, 4423-33, 2018 https://doi.org/10.1016/j.nanoen.2017.11.050) . The project was funded by NSTP KACST.
Another promising nanoarray based photo-anode was fabricated on large-surface by anodization followed by electrochemical deposition. An example of large-scale high density uniform nanoarrays fabricated by anodization is shown in figure 2. First high purity titanium metal surface completely anodized under optimized conditions to develop nanotube arrays. Then electrochemically Fe2O3 and ultra-low silver deposited under on the surface to make effective large-scale photanode Ag/α-Fe2O3/TiO2 with uniform morphology to absorb maximum visible light. The photo-electrochemical performance of nanoarrays is tested and reported in ACS Sustainable chemistry and Engineering (ACS Sustainable Chem. & Eng. 6, (2018) 12641–12649 https://pubs.acs.org/doi/abs/10.1021/acssuschemeng.7b02848).
Various other photo-anodes development is under process, such as metal vanadates. In an urgent communication, we reported hydrothermal synthesis of copper vanadates and its performance for OER (Scientific Reports 7 (2017), 14370). Also particle transfer method used to deposit high quality films of copper vanadates as oxygen evolution photocatalyst and AlSrTiO3 as hydrogen evolution photocatalysis showed bias-free overall water splitting (Video).
To improve the process of solar water splitting, our focus is materials development for OER photo-electrocatalyst with better charge separation and performance through surface passivation. Broad overview of this technology and its future prospect is deliberated in our recent article in Chemical Society Review(https://pubs.rsc.org/en/content/articlelanding/2019/cs/c8cs00987b#!divAbstract). Presently our team is working on new materials development such as semiconductor metal oxynitrides, vanadates and oxyhydroxides for improved PEC water splitting, photocatalytic and electrochemical CO2 conversion, electrochemical OER, and other significant reactions
Dr. Ahsanulhaq is contributing in this area through different ways such subject editor for International Journal of Hydrogen Energy, Editorial Board Member of Scientific Reports and Materials Research Bulletin making editorial decisions for over 100 articles annually related to new materials development for clean energy and related fields.
Overall Water Splitting