A Si photocathode protected and activated with a Ti and Ni composite film for solar hydrogen production

Abstract

An efficient, stable and scalable hybrid photoelectrode for visible-light-driven H2 generation in an aqueous pH 9.2 electrolyte solution is reported. The photocathode consists of a p-type Si substrate layered with a Ti and Ni-containing composite film, which acts as both a protection and electrocatalyst layer on the Si substrate. The film is prepared by the simple drop casting of the molecular single-source precursor, [{Ti2(OEt)9(NiCl)}2] (TiNipre), onto the p-Si surface at room temperature, followed by cathodic in situ activation to form the catalytically active TiNi film (TiNicat). The p-Si|TiNicat photocathode exhibits prolonged hydrogen generation with a stable photocurrent of approximately -5 mA cm(-2) at 0 V vs. RHE in an aqueous pH 9.2 borate solution for several hours, and serves as a benchmark non-noble photocathode for solar H2 evolution that operates efficiently under neutral-alkaline conditions.

Keywords: hydrogen evolution; photocatalysis; photosynthesis; silicon; water splitting.

Figure 1

Schematic representation of the preparation of a TiNi-modified p-Si electrode by a dual process: drop casting of TiNi_pre followed by in situ cathodic activation to form TiNi_cat for protection and catalytic activation of the p-Si photocathode. TiNi_pre structure is adopted from X-ray coordinates.

Figure 2

(a) Linear sweep voltammetry (LSV) scans of (i) FTO|TiNi_cat, (ii) FTO|e-Ni, (iii) FTO|TiO₂, and (iv) FTO in an aqueous buffer solution (0.1 m B_i, 1 m KCl, pH 9.2) at a scan rate of 1 mV s⁻¹. The inset shows the SEM image of FTO|TiNi_cat with a scale bar of 2 μm. (b) Chronoamperometric traces at an applied potential of −0.6 V vs. RHE.

Figure 3

(a) XANES spectra and (b) Fourier-transformed EXAFS spectra collected from the Ni K-edge of (i) TiNi_pre, (ii) TiNi_cat, (iii) NiO, (iv) Ni(OH)₂, and (v) Ni foil.

Figure 4

(a) LSV scans measured in an aqueous pH 9.2 electrolyte solution (0.1 m B_i and 1 m KCl) under chopped solar light irradiation (AM 1.5G) with a scan rate of 5 mV s⁻¹. (b) Chronoamperometry of photocathodes recorded at 0 V vs. RHE under solar light irradiation (AM 1.5G) for 4 h.

Figure 5

A comparison of the electrochemical profile of FTO|TiNi_cat and FTO|Pt with the PEC profile of p-Si|TiNi_cat and p-Si|Pt to understand the PEC mechanism and factors limiting performance. LSV scans of FTO|Pt, FTO|TiNi_cat, and FTO electrodes for electrocatalytic HER (dark reaction) at 1 mV s⁻¹, and of p-Si|Pt photocathode and p-Si|TiNi_cat recorded under chopped solar light irradiation (AM 1.5G) at 5 mV s⁻¹. Experiments were conducted in an aqueous pH 9.2 solution (0.1 m B_i and 1 m KCl). (i) and (iii) indicate the electrocatalytic proton reduction current measured at FTO|TiNi_Cat and FTO|Pt, respectively, at the p-Si conduction band potential of −0.6 V vs. RHE; (ii) shows the photocurrent of p-Si|Pt recorded at 0 V vs. RHE under simulated solar light irradiation (AM 1.5G).