Ultrahigh-current-density niobium disulfide catalysts for hydrogen evolution

Area of Science:

• Materials Science
• Electrochemistry
• Catalysis

Background:

• Metallic transition metal dichalcogenides (TMDs) are recognized catalysts for the hydrogen evolution reaction (HER).
• Existing 2D TMD catalysts exhibit lower current densities compared to industrial platinum and iridium electrolyzers.
• There is a need for highly efficient and cost-effective HER catalysts.

Purpose of the Study:

• To synthesize and characterize a novel metallic 2H phase of niobium disulfide (2H Nb1+xS2) as an advanced HER catalyst.
• To evaluate the catalytic performance of 2H Nb1+xS2 in terms of overpotential, Tafel slope, and current density.
• To investigate the theoretical underpinnings of the enhanced HER activity in 2H Nb1+xS2.

Main Methods:

• Synthesis of metallic 2H Nb1+xS2 (x ≈ 0.35) with excess niobium.
• Electrochemical evaluation of the HER catalytic activity, including current density and overpotential measurements.
• Theoretical calculations to determine the hydrogen adsorption free energy on Nb-terminated surfaces.

Main Results:

• The synthesized 2H Nb1+xS2 demonstrated exceptionally high current densities exceeding 5,000 mA cm-2 at approximately 420 mV vs. RHE.
• An exchange current density of ~0.8 mA cm-2 and a turnover frequency of ~0.2 s-1 were observed for 2H Nb1.35S2.
• An electrolyzer utilizing a 2H Nb1+xS2 cathode achieved current densities of 1,000 mA cm-2.
• Theoretical analysis indicated a near-thermoneutral hydrogen adsorption free energy on Nb-terminated 2H Nb1+xS2 surfaces.

Conclusions:

• Metallic 2H Nb1+xS2 is a highly effective catalyst for the hydrogen evolution reaction.
• The material's performance surpasses that of many existing 2D TMD catalysts and approaches industrial standards.
• The favorable hydrogen adsorption energetics suggest 2H Nb1+xS2 is a promising candidate for practical electrolyzer applications.