Maximizing urea-/hydrazine-assisted electrolytic hydrogen production by defective nickel copper selenide nanostructures

Abstract

Replacing the formidable oxygen evolution reaction (OER) with other oxidizable species is an appealing approach to attain highly efficient hydrogen (H₂) generation with a lower potential. Accordingly, the kinetically favorable electrooxidation reaction of urea or hydrazine molecule can increase the return on energy profiteering and prevent pollutant emission. Thus, opening up an innovative direction to replace the sluggish OER and generate high-purity H₂ gas via an energy-saving approach. Thus, constructing highly efficient and stable bifunctional electrodes/electrocatalysts is a key to realize economical and sustainable H₂ production. In this work, we developed defect-enriched two-dimensional (2D) heterogeneous nickel copper selenide (D/Ni-Cu-Se) on a conductive Ni foam (NF) scaffold as an integrated bifunctional electrocatalytic electrode for energy-saving for H₂ production. The self-supported D/Ni-Cu-Se/NF electrode with a regulated interfacial property and abundant metal defects is fabricated through a hydrothermal approach and a metal-defect engineering route. The thus-prepared electrode exhibits a high electrocatalytic performance for both hydrogen evolution reaction (HER) and urea oxidation reaction (UOR) in a 1.0 M KOH electrolyte, achieving the catalytic current density of 10 mA cm⁻² at a potential of 87.7 mV and 1.335 V vs. RHE, respectively. In relation, the two-electrode urea-water electrolyzer and hydrazine-water electrolyzer utilizing the bifunctional D/Ni-Cu-Se/NF as both the cathode and anode electrodes reveal a cell voltage of ∼ 1.395 V and 0.268 V at 10 mA cm⁻² in 1.0 M KOH/0.33 M urea and 1.0 M KOH/0.25 M hydrazine, respectively, which is much less than that of conventional water electrolysis (1.572 V). The implemented electrolyzer systems consequently endow high long-term durability over 48 h of continuous electrolysis, indicating that the defect-rich D/Ni-Cu-Se/NF can serve as a potential bifunctional electrocatalyst with an outstanding electrolysis performance and excellent stability for H₂ generation. Indeed, such a novel bifunctional electrode configuration and corresponding electrolysis performances are much desired for energy-saving electrolytic H₂ production and pave the way for exploring highly efficient and robust electrodes.