Thickness-dependent photoelectrochemical properties of a semitransparent Co₃O₄ photocathode

Abstract

Co3O4 has been widely studied as a catalyst when coupled with a photoactive material during hydrogen production using water splitting. Here, we demonstrate a photoactive spinel Co3O4 electrode grown by the Kirkendall diffusion thermal oxidation of Co nanoparticles. The thickness-dependent structural, physical, optical, and electrical properties of Co3O4 samples are comprehensively studied. Our analysis shows that two bandgaps of 1.5 eV and 2.1 eV coexist with p-type conductivity in porous and semitransparent Co3O4 samples, which exhibit light-induced photocurrent in photoelectrochemical cells (PEC) containing the alkaline electrolyte. The thickness-dependent properties of Co3O4 related to its use as a working electrode in PEC cells are extensively studied and show potential for the application in water oxidation and reduction processes. To demonstrate the stability, an alkaline cell was composed for the water splitting system by using two Co3O4 photoelectrodes. The oxygen gas generation rate was obtained to be 7.17 mL·h−1 cm−1. Meanwhile, hydrogen gas generation rate was almost twice of 14.35 mL·h−1·cm−1 indicating the stoichiometric ratio of 1:2. We propose that a semitransparent Co3O4 photoactive electrode is a prospective candidate for use in PEC cells via heterojunctions for hydrogen generation.

Experimental Study of Precursor Concentration the Co3O4 Thin Films Used as Solar Absorbers

“…It is clear is that the intensity and the refinement of this peak increase with increasing molar concentration, so we can conclude that the increase in molar concentration improves the crystallinity of the material. The results found are in perfect agreement with the work of Patel et al [15], where the prepared Co3O4 films have different thicknesses (from 70 nm to 230 nm) on the FTO substrate by sputtering. Hamdani et al [16], who prepared thin films of Co3O4 by the spray pyrolysis technique found a preferential orientation according to the plan (311) and obtained a single phase for the films of Co3O4, while Avila et al [13] observed the appearance of some secondary phases corresponding to CoO and Co2O3.…”

Outstanding stability and photoelectrochemical catalytic performance of (Fe, Ni) co-doped Co3O4 photoelectrodes for solar hydrogen production

“…Deposition methods for Co3O4 thin films include sol-gel [25], chemical vapor deposition CVD [26], dip coating [27], pulsed laser [28], spurting technique [29]. Moreover, Co3O4 has a dualbandgap structure, offering separate band states, which is beneficial for thermalization-related losses in the hydrogen generation powered by sunlight [30]. Finally, it is earth-abundant [31], environmentally friendly [32],…”

Renewable energy conversion using nano- and microstructured materials

“…The Beilstein Journal of Nanotechnology thematic issue “Nano- and microstructures for energy conversion: materials and devices” provides insights into the latest developments in the related fields. Besides a focus on solar-cell concepts [1–5], it also addresses light harvesting by solar fuel production [6–7], and energy storage by batteries [8].…”

“…Nanostructured materials can be synthesized by a huge variety of approaches, extending from self-assembled structures [9], over various lithographic techniques [10] and imprinting methods [11], to different crystallization routes [12]. The thematic issue “Nano- and microstructures for energy conversion: materials and devices” covers the photo-electrochemical growth of platinum catalysts at plasmonic hot spots [6], the laser-assisted local growth of chalcopyrite absorbers [4], the preferential reactive ion etching of silicon by morphological anisotropies [5], the oxidation of copper nanoparticles resulting in nanoporous cobalt oxide photocathodes [7], and an approach in which silicon nanoparticles are embedded in an amorphous carbon matrix [8].…”

“…Particularly in photovoltaics, they may be prone to increased recombination losses. For other applications, such as water splitting, porous materials may however be desired as the example of Co 3 O 4 photocathodes in [7] shows.…”