Fabrication of a novel Ni3N/Ni4N heterojunction as a non-noble metal co-catalyst to boost the H2 evolution efficiency of Zn0.5Cd0.5S

Abstract

Previous studies have shown that auxiliary catalysts play a significant role in improving the activity and reliability of semiconductor photocatalysis for photocatalytic H₂ production. However, designing an efficient and low-cost auxiliary catalyst to replace expensive noble metals has been a major challenge. In our study, we synthesized a non-noble metal co-catalyst Ni₃N/Ni₄N (Ni_xN) by a two-step method. Upon loading 2% Ni_xN on Zn_0.5Cd_0.5S (ZCS), the photocatalytic activity of 2% Ni_xN/ZCS greatly improved. The corresponding H₂ evolution rate was about 241.3 mmol h⁻¹ g⁻¹, which was obtained in 0.35 M Na₂S/0.25 M Na₂SO₃. This value is about 33 times higher than that of pure ZCS, 12 times higher than that of 2% Pt on ZCS and 3 times higher than that of 2% Ni₃N/ZCS. When the concentration of Na₂S/Na₂SO₃ was increased to 1.05 M/0.75 M, the H₂ production rate of 2% Ni_xN/ZCS reached 297.6 mmol h⁻¹ g⁻¹ under visible light irradiation (λ > 420 nm), and the quantum efficiency (QE) was 43.8% at 420 nm. The H₂ production efficiency of 2% Ni_xN/ZCS is the highest H₂ evolution efficiency among ZCS-based photocatalysts reported so far. The introduction of the Ni₃N/Ni₄N heterojunction could efficiently accelerate the migration of photocarriers and delay the recombination of electron–hole pairs.