Photoelectrochemical hydrogen production in water using a layer-by-layer assembly of a Ru dye and Ni catalyst on NiO

摘要

Capture and conversion of sunlight into the storable energy carrier H2 can be achieved through photoelectrochemical water splitting using light-absorbing cathodes and anodes bearing H2 and O2 evolving catalysts. Here, we report on the development of a dye-sensitised p-type nickel oxide (NiO) photocathode with a hexaphosphonated Ru(2,2′-bipyridine)3 based dye (>RuP3) and a tetraphosphonated molecular [Ni(P2N2)2]²⁺ type proton reduction catalyst (>NiP) for the photoreduction of aqueous protons to H2. A layer-by-layer deposition approach was employed, using Zr⁴⁺ ions to link the phosphonate units in >RuP3 and >NiP in a supramolecular assembly on the NiO photocathode. This approach keeps the dye in close proximity to the catalyst and semiconductor surface, but spatially separates >NiP from NiO for advantageous electron transfer dynamics. The NiO|>RuP3–Zr⁴⁺–>NiP electrodes generate higher photocurrents and are more stable than photocathodes with >RuP3 and >NiP co-immobilised on the NiO surface in the absence of Zr⁴⁺ cations linking dye and catalyst. The generation of H2 with the NiO|>RuP3–Zr⁴⁺–>NiP hybrid electrode in pH 3 aqueous electrolyte solution during irradiation with a UV-filtered solar light simulator (λ > 400 nm, 100 mW cm^–2, AM1.5G) has been confirmed by gas chromatography at an underpotential of 300 mV (Eappl = +0.3 V vs. RHE), demonstrating the potential of these electrodes to store solar energy in the chemical bond of H2.