The electrochemical water splitting presents a sustainable way to produce green hydrogen by electrocatalytic reduction of water [1–4]. The photocatalytic (PC) and photoelectrochemical (PEC) systems by utilizing the solar energy is a promising example of artificial photosynthesis to produce hydrogen (H2) and oxygen (O2) gases in a single cell [5,6]. Researchers have made tremendous efforts to produce H2 and O2 by individual PC and PEC water splitting systems. PC process suffers from fast recombination rate of photogenerated electron-hole pairs and mixed gases (H2 and O2) production in a single cell. The photocatalysts nanoparticle (NPs) dispersed in neutral media electrolyte provide a medium to integrate PC and PEC water splitting process. Light illuminated photocatalysts generate reactive intermediate species in electrolyte such as hydroxyl radicals (.OH), superoxide anion (O2.), and hydrogen peroxide (H2O2), which act as an in-situ oxidizing agent to oxidize the water molecule on the photoanode surface and reduces the overpotential for oxygen evolution reaction (OER) kinetics.
The WO3-BiVO4 heterojunction based photoanodes have presented superior PEC water oxidation activity due to enhanced photogenerated charge-carriers transport property of WO3 and promising visible region photon absorption response of BiVO4 [7,8]. WO3- BiVO4 heterojunction is synthesized by spin-coating WO3 film onto the FTO coated transparent glass substrate, after that BiVO4 layer spin-coating onto the WO3 film. The g-C3N4-AQCOOH photocatalyst was synthesized by mixing the g-C3N4 with the solution of anthraquinone acetic acid and acetonitrile and further washed and dried. The photoanode (WO3-BiVO4) compartment electrolyte is aqueous 1 mg/mL g-C3N4-AQCOOH photocatalyst dispersion (in 0.1 M PBS) and cathode (Pt foil) compartment electrolyte is 0.1 M PBS (20 mL). Both the compartment is separated by NAFION 117 membrane. Light illumination over g-C3N4-AQCOOH NPs showed .OH radical and H2O2 production in photoanode compartment and confirmed by fluorescence probe and HPLC method. Integrated PEC water splitting with PC system showed ~ 2 times higher photocurrent density (~3.9 mA/cm2) than only PEC water splitting at 1.23 V vs. RHE low applied potential under illumination condition, with long-time stability (~ 12 hours). The light illuminated g-C3N4-AQCOOH NPs produced reactive intermediates such as .OH free radicals and H2O2 capable of promoting the OER kinetics at the photoanode surface. The application of g-C3N4-AQCOOH NPs to facilitate the water oxidation reaction showed a new paradigm for sustainable and green H2 fuel provision for enhanced PEC water splitting.
References:
[1] Dixit RJ, Bhattacharyya K, Ramani VK, Basu S. (2021). Electrocatalytic hydrogenation of furfural using non-noble-metal electrocatalysts in alkaline medium. Green Chem;23:4201–12.
[2] De BS, Singh A, Elias A, Khare N, Basu S. (2020). An electrochemical neutralization energy-assisted membrane-less microfluidic reactor for water electrolysis. Sustain Energy Fuels;4:6234–44.
[3] Biswajit S. De, Pawan Kumar, Neeraj Khare, Jing-Li Luo, Anastasia Elias SB. (2021) Microfabrication of the Ammonia Plasma-Activated Nickel Nitride− Nickel Thin Film for Overall Water Splitting in the Microfluidic Membraneless Electrolyzer;4:9639–52.
[4] Samir De B, Cunningham J, Khare N, Luo JL, Elias A, Basu S. (2022). Hydrogen generation and utilization in a two-phase flow membraneless microfluidic electrolyzer-fuel cell tandem operation for micropower application. Appl Energy;305:117945.
[5] Singh A, Tejasvi R, Karmakar S, Basu S. (2021). α-Fe2O3 nanorods decorated with NiMnO3 co-catalyst as photoanode for enhanced oxygen evolution reaction in photoelectrochemical water splitting. Mater Today Commun;27:102231.
[6] Dixit RJ, Singh A, Ramani VK, Basu S. (2021). Electrocatalytic hydrogenation of furfural paired with photoelectrochemical oxidation of water and furfural in batch and flow cells. React Chem Eng:2342–53.
[7] Singh A, Karmakar S, Basu S. (2021). Role of sputtered WO3 underlayer and NiFeCr-LDH co-catalyst in WO3–BiVO4 heterojunction for enhanced photoelectrochemical water oxidation. Int J Hydrogen Energy;46:39868–81.
[8] Singh A, Sarma SK, Karmakar S, Basu S. (2021). Photocatalytic H2O2 generation assisted photoelectrochemical water oxidation for enhanced BiVO4 photoanode performance. Chem Eng J Adv;8:100142.
