Exploring Boron-Doped Diamond for Energy Conversion and Storage Applications

Boron-doped diamond (BDD) has emerged as a promising material for advanced energy applications, particularly in solar cell and battery fields. Applications explored include energy conversion in dye-sensitized solar cells (DSSCs) and perovskite solar cells (PSCs), as well as energy storage in aqueous batteries (ABs). In solar cell technology, BDD serves as an effective p-type semiconductor, enhancing charge carrier mobility and reducing recombination losses, thereby improving overall cell efficiency. Its remarkable optical transparency and high thermal conductivity further contribute to its suitability for high-performance photovoltaic systems. In battery technology, BDD's exceptional chemical stability and high electrical conductivity make it an ideal candidate for electrodes. The material's robustness and ability to operate under extreme conditions offer significant advantages in terms of battery longevity and performance. ABs, which are based on a saline aqueous electrolyte and a carbon-based electrode material, possess a narrow electrochemical stability window (1.23 V) in commonly used salt concentrations (ca. 1M) of aqueous electrolyte solutions. This window can be significantly enlarged by using highly concentrated “water–in–salt” (WIS) electrolytes [1] in combination with an appropriate electrode material. For this application, i.e. ABs with highly corrosive environments, the suitable electrode material appears to be BDD due to its excellent chemical stability and wide potential window compared to other carbon-based materials.<br/><br/>This work examines the basic electrochemical characterization of BDD electrodes and focuses on <i>in situ</i> Raman spectroelectrochemical (SEC) investigation in a standard glass cell [2], and in a micro-droplet setup [3]. This non-destructive, real-time method combining Raman spectroscopy and electrochemistry is employed to study the structural, chemical, and electronic changes of an electrode material as a result of different potentials applied. BDD films were grown by microwave plasma-enhanced chemical vapor deposition with different quality (sp² carbon content) and boron doping levels (B/C ratio in the gas phase). In BDD films containing a high amount of sp² carbon, modes belonging to these carbonaceous phases changed their intensities in the potential range of -1.0 V to 1.5 V vs. Ag/AgCl. Specifically, the intensity of the D, G, and D′ Raman peaks increased in the cathodic direction, while bleaching of these peaks was observed in the anodic direction. Modes belonging to sp³ carbon and the boron incorporated into the diamond lattice exhibited no changes with the applied potential, suggesting the high stability of this material in the bulk. The trend of a decreasing potential stability window of BDD with increasing content of sp² carbon at the same doping level was observed using cyclic voltammetry. In the case of WIS electrolytes, the dependence of the potential stability window size of highly doped BDD is surprisingly opposite, i.e., with increasing sp² carbon content, the potential window is wider. The influence of BDD stability with various sp² carbon content and boron doping levels in WIS electrolytes, determined by <i>in situ</i> Raman SEC, will be discussed.<br/><br/><u>References</u><br/>[1] ZAFAR, Z.A., ABBAS, G., ŠILHAVÍK, M., et al. Reversible anion intercalation into graphite from aluminum perchlorate “water–in–salt” electrolyte, <i>Electrochimica Acta,</i> 2022, vol. 404, pp. 139754.<br/>[2] VLČKOVÁ ZIVCOVÁ, Z., FRANK, O., PETRÁK, V., et al. Electrochemistry and in situ Raman spectroelectrochemistry of low and high quality boron doped diamond layers in aqueous electrolyte solution, <i>Electrochimica Acta,</i> 2013, vol. 87, pp. 518-525.<br/>[3] VLČKOVÁ ZIVCOVÁ, Z., BOUŠA, M., VELICKÝ, M., et al. In Situ Raman Microdroplet Spectroelectrochemical Investigation of CuSCN Electrodeposited on Different Substrates, <i>Nanomaterials,</i> 2021, vol. 11, pp. 1256.