Application of Calcium Bismuthate (CaBi6O10) as a Photoelectrode for PEC Water Splitting

Basha, Shaik Khadar and Meduri, Praveen (2018) Application of Calcium Bismuthate (CaBi6O10) as a Photoelectrode for PEC Water Splitting. Masters thesis, Indian Institute of Technology hyderabad.

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Abstract

Water splitting is a photocatalytic (PC) or photoelectrochemical (PEC) reaction process which utilizes sunlight and water to produce hydrogen and oxygen gases as products under certain conditions. It employs photoactive semiconductors as catalysts for the reaction. CaBi6O10 is one such photocatalyst which has recently been reported as a promising photoanode for PEC water splitting. This thesis presents an overview of the sequence of water splitting processes in general and discusses factors such as semiconductor band bending and band gap which are essential for it. The conditions of water splitting (band edge and band gap requirements) are also obtained and are reasoned with the driving force of each of the individual processes. Chapter 1 also covers the need for PEC hydrogen as an energy carrier and the challenges associated with its renewable way of production. The technology for storing hydrogen is itself a subject matter in research which has its own challenges when it comes to collecting hydrogen from large-scale operated PEC devices. The progress in this area can be accelerated if the performance of different photoelectrode materials can be compared directly with one another using the literature reported values. Therefore, the need for maintaining standard experimental conditions in case of certain parameters (such as incident light radiation) is also discussed. The second part of the thesis focuses on CaBi6O10 calcium bismuthate as a photoanode electrode. Narrow band gap, broader conduction band and suitable band positions are some of the inherent characteristics of CaBi6O10 effective for water splitting. The samples were prepared by dip coating a precursor solution of Ca+2 and Bi+3 on FTO glass and are tested in an electrochemical system. The results obtained indicated that the morphology and uniform deposition of CaBi6O10 films is easily effected by the synthesis conditions. That is why, the obtained current density values differed even in between two samples prepared by using the same method. The highest photocurrent density which we obtained was 0.3 mA/cm2 at 0.7 V vs. RHE. Also, the photocurrents remained stable only for a small range of potential bias applied.

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