To meet the growing energy demand, developing a clean, cheap, and efficient renewable energy technology is imminent for the mankind. One such technology involves converting solar energy into electricity. In this seminar, two technologies would be discussed, one is the cost-effective dye-sensitized solar cells (DSSCs) and other is photo-rechargeable supercapacitors.
Generally, dye adsorption on TiO2 is performed by soaking FTO/TiO2 electrodes in dilute non-aqueous dye solution for 12 to 48 h.1,2 In Chapter-1, a quick and novel electrosorption-assisted dye-staining process was discussed to develop a photoanode in less than an hour of time. It is an entropy driven technique. To demonstrate the suitability of this technique for both metal and metal-free dyes, two commercially available metal-based dyes (N719 and Z907) and two metal-free dyes D2d (name) and T-SB-C (name) were chosen. Through this process, the dye loading realized on the photoanodes was more than that of the conventional soaking process. In the case of N719 dye, dye loading was enhanced about 100% from 0.58 x 10-7 to 1.21 x 10-7 mol cm-2, and power conversion efficiency (PCE) by 35%.3 Transient absorption measurement was used to probe the reason behind improved efficiency of the DSSC’s photoanode made of electrosorption, which confirms categorically the increased dye loading to be responsible for the enhancement in the performance of the DSSCs.
Density functional theory (DFT) and the time-dependent DFT approach were used to design new state-of-the-art metal-free dyes and to get insight into the photophysical properties of the dyes. Panchromatic adsorption, tapping IR radiation of the sun’s spectra along with the entire visible region, is one of the ways to improve the PCE of DSSCs. In this context, designing of the metal-free organic dyes through molecular engineering of donor and acceptor moieties was performed to investigate the structure-property relationship using the theoretical approach (Chapter-2A4 and 2B5). Further, In Chapter-3, a robust way to interpret the quantitative structure–activity relationship (QSPR) model of 1448 dye molecules by combining three different properties, such as structural, quantum, and experimental, in predicting the PCE of DSSCs via Machine Learning (ML) and computational methods was explored. Random forest emerged as the best model with a prediction accuracy of 95.31% and a root mean squared error of 0.802. The developed ML model gives an insight on various descriptors having dominant contributions toward PCE, and this has been used to propose novel dye molecules for DSSCs with improved efficiency6.
In addition, we have also focused in developing electrode materials, from eco-benign sources, for the energy storage system such as supercapacitor (SCs). The importance of asymmetric design to improve the wide operating voltage window thereby high energy density of aqueous SC is highlighted in Chapter-4A. An asymmetric SC comprising of a porous 3D cubical shaped Prussian blue (PB) decorated carbon derived from tamarind seeds (ACTS-800) (PB@ACTS-800) as a positive electrode and ACTS-800 as negative electrode in 3 M KNO3 electrolyte is fabricated. Impressively, the resulting ACTS-800//PB@ACTS-800 (1:2) asymmetric SC demonstrated a broad electrochemical stable voltage window of 2.2 V in aqueous medium with high energy density of 60 Wh/kg at power of 551 W/kg. The reported metrics are much superior to most of the carbon/carbon SCs operating in aqueous medium. Further, Chapter-4B was focused on the photo rechargeable supercapacitor by combining the energy conversion and storage in a single-cell using metal-oxynitrides (MON). MON has demonstrated higher surface area of 244 m2/g, and exhibited capacitance of 118 F/g (@10 mV/s) in dark condition. A good capacitive response of 138 F/g (10 mV/s) with a wide voltage window of 1.8 V (which is one of the highest operating voltages achieved so far in the existing literature) also realized in 2E mode against Zn foil as counter electrode under light (590 nm) condition.
References:
1 H. Seo, M. K. Son, I. Shin, J. K. Kim, K. J. Lee, K. Prabakar and H. J. Kim, Electrochim. Acta, 2010, 55, 4120–4123.
2 M. A. Mamun, Q. Qiao and B. A. Logue, RSC Adv., 2018, 8, 31943–31949.
3 G. R. Kandregula, J. Sivanadanam and K. Ramanujam, Electrochim. Acta, 2020, 349, 136344.
4 G. R. Kandregula, S. Mandal, G. Prince, S. K. Yadav and K. Ramanujam, New J. Chem., 2020, 44, 4877–4886.
5 G. R. Kandregula, S. Mandal and K. Ramanujam, J. Photochem. Photobiol. A Chem., 2021, 410, 113161.
6 G. R. Kandregula, D. K. Murugaiah, N. A. Murugan and K. Ramanujam, New J. Chem., 2022, 46, 4395–4405.