Why Can a New Nickel–Copper Catalyst Make Hydrogen Production from Water Electrolysis More Efficient and Less Energy-Intensive?

So, the nickel–copper catalyst works in a really clever way. Basically, the material combines amorphous nickel sulfide with crystalline copper, which creates a sort of “teamwork” at the atomic level. The sulfur atoms carry positive charges that speed up the first electron transfer in the hydrogen evolution reaction, while the copper sites are tuned to balance how strongly hydrogen intermediates stick and release, making the whole process more efficient. On top of that, the interface between the two components actually restructures itself a bit during the reaction, which helps weaken the binding of oxygen intermediates and makes oxygen evolution faster. Practically speaking, this means you can run water electrolysis at lower voltage — like 1.49 V for a decent current density — which translates to less energy use compared to traditional platinum or iridium catalysts. So yes, with this approach, producing hydrogen becomes more energy-efficient and potentially cheaper, and it brings us closer to scaling up green hydrogen production using non-precious metals.

The nickel-copper composite catalyst operates via a synergistic triple mechanism rooted in structural and electronic tuning. Amorphous nickel sulfide (a-NiSₓ) and crystalline copper (c-Cu) form a heterostructure where sulfur atoms in a-NiSₓ accumulate positive charge, accelerating the first electron-transfer kinetics of the hydrogen evolution reaction (HER)—a key bottleneck in alkaline HER. Meanwhile, c-Cu optimizes the d-band center of active sites: a balanced d-band structure ensures moderate adsorption-desorption of hydrogen intermediates (H*), avoiding the inefficiency caused by overly strong (blocking active sites) or weak (insufficient H* capture) adsorption, which is a common flaw in single-component catalysts. At the heterointerfaces, strong electronic interactions trigger surface reconstruction, weakening the adsorption of oxygen evolution reaction (OER) intermediates (e.g., *OH, *O), thus lowering the energy barrier for the sluggish four-proton-coupled electron transfer in OER.

Electron structure tuning is pivotal here: it modulates the charge distribution of active sites and the d-band center, directly optimizing the binding energy with reaction intermediates—a core factor determining catalytic efficiency, which traditional catalysts often fail to regulate precisely. Practically, the 1.49 V cell voltage at 10 mA/cm² is notably lower than that of precious-metal catalysts (e.g., Pt/C for HER + IrO₂ for OER, typically requiring ~1.6 V), drastically reducing energy consumption. This approach is close to large-scale green hydrogen production: it uses low-cost, earth-abundant non-precious metals (avoiding the scarcity/cost issues of Pt, Ir, Ru) and is compatible with anion exchange membrane electrolyzers (a mainstream device for green hydrogen). However, challenges like long-term stability under high current densities still need addressing for full industrial adoption.

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The integration of amorphous nickel sulfide with crystalline copper in electrocatalytic materials represents a significant advancement in alkaline water electrolysis for hydrogen production. This composite catalyst addresses intrinsic limitations of conventional non-precious metal catalysts through sophisticated electronic structure modulation. The amorphous nickel sulfide phase exhibits abundant unsaturated coordination sites and defective structures, while the crystalline copper framework provides electrical conductivity and structural stability. Their combination creates heterogeneous interfaces that induce charge redistribution, fundamentally altering reaction pathways for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER).

The enhanced catalytic performance originates from three synergistic mechanisms. Sulfur atoms in nickel sulfide accumulate positive charges that dramatically accelerate the initial electron transfer kinetics in HER, addressing the slow elementary step that plagues alkaline electrolysis. Copper sites with optimized d-band structure regulate the adsorption/desorption behavior of hydrogen intermediates (H), achieving neither too strong nor too weak bonding that would compromise thermodynamic efficiency. Most remarkably, the strong interfacial interaction between amorphous and crystalline phases triggers surface reconstruction during operation, weakening the adsorption strength of critical oxygen-containing intermediates (O, *OOH) in OER and thus facilitating the challenging four-proton-coupled electron transfer process.

Practically, this electronic structure engineering enables exceptional operational efficiency. The material demonstrates overall water splitting capability at just 1.49V cell voltage to achieve 10 mA/cm² current density in anion exchange membrane electrolyzers – approaching the performance of precious-metal catalysts (IrO₂, Pt/C) that require similar voltages but at dramatically reduced cost. This voltage reduction translates directly to lower energy consumption, potentially decreasing electricity usage by 15-20% compared to conventional non-precious catalysts.

For large-scale green hydrogen production, this technology demonstrates several advantageous characteristics: compatibility with industrial anion exchange membrane systems, reduced overpotential losses, and elimination of precious metal dependence. While durability testing under commercial operating conditions remains ongoing, the material's innovative amorphous-crystalline heterostructure provides atomic-level insights for designing cost-effective electrocatalysts. This development represents a crucial step toward economically viable green hydrogen, potentially accelerating the transition to renewable energy storage and decarbonizing industrial sectors that currently rely on fossil fuel-derived hydrogen.