Nickel incorporated graphitic carbon nitride supported copper sulfide for efficient noble-metal-free photo-electrochemical water splitting

Trioctylphosphine Oxide (TOPO)-Assisted Facile Fabrication of Phosphorus-Incorporated Nanostructured Carbon Nitride Toward Photoelectrochemical Water Splitting with Enhanced Activity

Designing nanostructured arrays of two-dimensional surfaces and interfaces is a versatile approach to increasing their photoelectrochemical activity. Here, phosphorus (P)-incorporated nanostructured carbon nitride (h-PCN) with an enlarged surface area is fabricated by employing trioctylphosphine oxide (TOPO) as a dopant precursor for visible-light-driven photoelectrochemical water splitting to produce hydrogen. The structural, morphological, and electronic properties of the photocatalyst have been characterized through various physicochemical techniques. We show that the incorporation of P into the g-C₃N₄ framework enhances light absorption over broad regimes, charge separation, and migration, as well as the specific surface area, showing excellent photocurrent enhancement (5.4 folds) in the cathodic direction as compared to bulk g-C₃N₄. Moreover, the photocathode shows 3.3-fold enhancement in current at zero biased potential. Without using any cocatalyst, the photoelectrodes produced 27 μmol h^-1 of H₂ and 13 μmol h^-1of O₂ with 95% faradic efficiency. The excellent photoelectrochemical behavior toward water-splitting reactions by the photoelectrode is attributed to the synergistic effect of P incorporation and active sites emerging from the nanostructured architecture of the material. This work demonstrates the facile fabrication of nanostructured P-incorporated g-C₃N₄ toward water-splitting reactions to produce hydrogen without using a cocatalyst in a simple and cost-effective way.

Water Splitting with Enhanced Efficiency Using a Nickel-Based Co-Catalyst at a Cupric Oxide Photocathode

Homemade non-critical raw materials such as Ni or NiCu co-catalysts were added at the photocathode of a tandem cell, constituted by photoelectrodes made of earth-abundant materials, to generate green solar hydrogen from photoelectrochemical water splitting. Oxygen evolving at the Ti-and-P-doped hematite/TCO-based photoanode and hydrogen at the cupric oxide/GDL-based photocathode are separated by an anion exchange polymer electrolyte membrane placed between them. The effect of the aforementioned co-catalysts was studied in a complete PEC cell in the presence of the ionomer dispersion and the anionic membrane to evaluate their impact under practical conditions. Notably, different amounts of Ni or NiCu co-catalysts were used to improve the hydrogen evolution reaction (HER) kinetics and the overall solar-to-hydrogen (STH) efficiency of the photoelectrochemical cells. At −0.6 V, in the bias-assisted region, the photocurrent density reaches about 2 mA cm−2 for a cell with 12 µg cm−2 of Ni loading, followed by 1.75 mA cm−2 for the cell configuration based on 8 µg cm−2 of NiCu. For the best-performing cell, enthalpy efficiency at −0.4 V reaches a first maximum value of 2.03%. In contrast, the throughput efficiency, which is a ratio between the power output and the total power input (solar + electric) provided by an external source, calculated at −1.225 V, reaches a maximum of 10.75%. This value is approximately three times higher than the best results obtained in our previous studies without the use of co-catalysts at the photocathode.