Coupling furfural oxidation for bias-free hydrogen production using crystalline silicon photoelectrodes

Abstract

To commercialize the technology of photoelectrochemical hydrogen production, it is essential to surpass the US. Department of Energy target of 0.36 mmol h^-1 cm^-2 for 1-sun hydrogen production rate. In this study, we utilize crystalline silicon, which can exhibit the highest photocurrent density (43.37 mA cm^-2), as the photoelectrode material. However, achieving bias-free water splitting (>1.6 V) remains challenging due to the intrinsic low photovoltage of crystalline silicon (0.6 V). To address this limitation, we replace water oxidation with low-potential furfural oxidation, enabling not only bias-free hydrogen production but also dual hydrogen production at both the cathodic and anodic sides. This approach results in a record 1-sun hydrogen production rate of 1.40 mmol h^-1 cm^-2, exceeding the Department of Energy target by more than fourfold.

Fig. 1. Schematic diagram of PEC H₂ production using the PtC/Ni/c-Si photocathode.

a LSV curves of aldehyde oxidation, water oxidation, and water reduction. b Bias-free PEC dual H₂ production system with the highly efficient PtC/Ni/c-Si photocathode.

Fig. 2. Schematic diagram of the PtC/Ni/c-Si photocathode and its performance.

a Fabrication scheme of the PtC/Ni/c-Si photocathode. b Absorption spectra of the IBC cell depending on the structure. c LSV curves of the PtC/Ni/c-Si photocathode. d Chronoamperometry measurement of the PtC/Ni/c-Si photocathode at 0.26 V vs. RHE. Changes in the thermal images of the encapsulated c-Si IBC cell in the atmosphere (e) and the PtC/Ni/c-Si photocathode in the electrolyte (f) under continuous light illumination. g Temperature profile of the encapsulated c-Si IBC cell in the atmosphere and the PtC/Ni/c-Si photocathode in the electrolyte. h Temperature-dependent current density‒voltage curves of the encapsulated c-Si IBC cell. i Temperature-dependent LSV curve of the PtC/Ni/c-Si photocathode. All PEC performances were measured under one sun illumination (AM 1.5 G) in 1 M NaOH. The error bars indicate the standard deviation based on three independent measurements. Source data are provided as a Source Data file.

Fig. 3. Characterization and furfural oxidation activities of the Cu wire catalyst.

a X-ray diffraction patterns of Cu wire and bare Cu. b HRTEM image of Cu wire. Inset: fast Fourier transform pattern. c SEM images of Cu wire and bare Cu. d LSV curves of Cu wire in 1 M NaOH with and without 50 mM furfural e The amount of reactant and products and carbon balance over time during the electrolysis at 0.3 V vs. RHE. f Furoic acid and H₂ Faradaic efficiency of Cu wire at 0.2‒0.3 V vs. RHE. All electrocatalytic activities were measured in 1 M NaOH with 50 mM furfural. The error bars indicate the standard deviation based on three independent measurements. Source data are provided as a Source Data file.

Fig. 4. Overall bias-free PEC H₂ production.

a LSV curves of furfural oxidation with HER, OER with HER using the PtC/Ni/c-Si photocathode, and LSV curves of OER with HER using the modularized PtC/Ni/c-Si photocathode in the two-electrode configuration. b Chronoamperometry of dual H₂ production using the PtC/Ni/c-Si photocathode at 0 V. c Produced H₂ and its Faradaic efficiency for dual H₂ production. d Mass spectra of collected gas from anode and cathode sides during the bias-free C₆H₅–CDO oxidation and HER. e H₂ production rate comparison with previously reported bias-free PEC H₂ production system. Biomass: Biomass oxidation reaction, IOR: iodide oxidation reaction, Dual photoelectrode (Photoanode║Photocathode). The experiments were conducted in 1 M NaOH with (for dual H₂ production) and without 50 mM furfural (for water splitting) in the two-electrode configuration under AM 1.5 G illumination. The error bars indicate the standard deviation based on three independent measurements. Source data are provided as a Source Data file.