Gradient‐Structuring Manipulation in Ni₃S₂ Layer Boosts Solar Hydrogen Production of Si Photocathode in Alkaline Media

Abstract

consists of a photocathode and photoanode to drive the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), separately. [5] To fulfill a practical PEC device, the photocathode needs to be placed in the same electrolyte as the photoanode. [6] It has long been known that HER is more favorable in acid than in alkaline solutions when taking the benchmark platinum-based catalysts as an example, due to the lower activation energy of the water dissociation step involved in acid HER. [7,8] Nevertheless, many of the potential photoanode materials and OER catalysts are easily photocorroded or chemically eroded in acidic solutions, [9][10][11] developing highly stable and active photocathode in alkaline solutions is in urgent demand for revolutionizing the hydrogen economy.As an earth-abundant and prevailing material for photovoltaic applications, silicon (Si) holds great perspective for PEC water splitting. [12,13] Specially, the p-type silicon (p-Si) has a suitable conduction band with respect to HER, but tethered by issues such as surface corrosion and sluggish kinetics. [13][14][15] One effectual strategy is to implement a conformal passivation layer to isolate Si from the electrolyte. This has been met with some success with metal oxides, such as TiO 2 [16,17] and NiO x , [18] but exhibiting an obvious trade-off Usingsilicon as a photocathode has long been considered as an ideal pathway toward cost-effective photoelectrochemical (PEC) solar hydrogen production. However, the trade-off between charge transfer efficiency and stability severely restricts the practical application of Si-based PEC devices in alkaline media. Herein, a facile thermo-electrodeposition process to integrate a gradient-structuring Ni 3 S 2 (G-Ni 3 S x O 2−x ) layer to simultaneously protect and act as a catalyst in Si photocathodes in alkaline solutions is reported. The G-Ni 3 S x O 2−x layer not only provides abundant active sites for the hydrogen evolution reaction but also promotes the charge separation and transport and mass transfer. Consequently, the as-fabricated Si photocathodes exhibit an excellent PEC activity under simulated AM1.5G illumination with a high onset potential of 0.39 V versus reversible hydrogen electrode (RHE) and a photocurrent density of −33.8 mA cm −2 at 0 V versus RHE, outperforming the state-of-the-art p-Si based photocathodes. Moreover, the G-Ni 3 S x O 2−x layer possesses a good interfacial contact with the Si substrate with negligible stress at the G-Ni 3 S x O 2−x /Si interface, affording a good durability of over 120 h at >30 mA cm −2 in alkaline media. This gradient-structuring strategy paves new way for engineering highly efficient and durable PEC devices.

Research on the Influence of the Interfacial Properties Between a Cu3BiS3 Film and an InxCd1−xS Buffer Layer for Photoelectrochemical Water Splitting

“…In the field of photocatalytic hydrogen production, one of the core problems that experts have been focusing on is how to improve the separation efficiency of photogenerated carriers. [ 39 ] However, we know that the reasonable design of the buffer layer can have a useful effect on charge separation. It is particularly important to evaluate the charge separation ability before hydrogen production experiments of photocathode Pt‐TiO 2 /In x Cd 1− x S/Cu 3 BiS 3 under sunlight.…”

Boosting the Electrochemical 5‐Hydroxymethylfurfural Oxidation by Balancing the Competitive Adsorption of Organic and OH− over Controllable Reconstructed Ni3S2/NiOx

“…[15] Ni 3 S 2 /NiO x -15 having the largest double-layer capacitance (C dl = 72.2 mF cm −2 ) also indicated that it had the most exposed catalytically active sites (Figure S30, Supporting Information). [16] The selectivity for HMFOR over the OER is another important issue because the latter is the predominant potential side reaction in alkaline electrolytes. The potential demand at the same current density was significantly reduced after adding 20 mm HMF to 1 m KOH (ΔE = 295 mV at j = 100 mA cm −2 ) (Figure S31, Supporting Information), implying that HMFOR on Ni 3 S 2 /NiO x -15 was more favorable than the OER.…”

Recent trends in photoelectrochemical water splitting: the role of cocatalysts

“…A gradient-structured Ni 3 S 2 (G-Ni 3 S x O 2−x ) layer was added via a thermoelectrodeposition method, which acts as a passivation layer as well as the PEC-HER catalyst coated over p-Si [Fig. 7e] 72 . In a 1 M NaOH aqueous solution, G-Ni 3 S x O 2-x /p-Si demonstrated extraordinary PEC performance, with a noteworthy onset potential (E op = 0.39 V RHE ) and a photocurrent density of −33.8 mA cm −2 at…”