The researchers, led by Aicheng Song and corresponding author Zhitao Han of the Marine Engineering College at Dalian Maritime University, together with colleagues at Harbin Engineering University, synthesized a family of nickel-modified copper-based metal-organic frameworks using a solvothermal method, in which the framework precursors are crystallized from a hot organic solvent. Metal-organic frameworks, or MOFs, are crystalline lattices in which metal ions or clusters are linked by organic ligands into highly ordered, porous architectures. Their appeal as catalyst precursors lies in two properties: their metal centers can be arranged with atomic precision, and their pores create an enormous internal surface area. The team then subjected these frameworks to calcination—heating under controlled conditions—to produce derivative catalysts in which the original structure transforms into a more robust, conductive form while retaining the porosity and bimetallic intimacy of the parent framework. By tuning the nickel content, they generated a series of samples designated by increasing nickel loading, culminating in the optimized catalyst labeled CuNi-2.

The performance figures reported for CuNi-2 are striking. At an applied potential of -1.0 volts versus a reversible hydrogen electrode, a standard reference condition in electrocatalysis, the catalyst achieved a Faradaic efficiency of 55.56 percent for multi-carbon products overall and 32.35 percent for ethylene specifically. Faradaic efficiency, also called Faraday efficiency, measures the fraction of electrical current that goes into making a given product rather than into competing side reactions; values above 50 percent for multi-carbon products on a MOF-derived copper system represent a meaningful advance. Equally important, the catalyst sustained its activity over 40 hours of continuous operation without significant degradation. Durability is often the Achilles heel of MOF-derived catalysts, which can restructure, sinter, or leach under the harsh reducing potentials required for carbon dioxide reduction, so a 40-hour stability test provides reassurance that the bimetallic architecture is not merely a transient arrangement of atoms but a genuinely robust catalytic system.

The central scientific insight of the study concerns the electronic interplay between nickel and copper. Through a battery of characterization techniques—including X-ray diffraction to determine crystal structure, scanning electron microscopy and energy dispersive X-ray spectroscopy to map morphology and elemental distribution, X-ray photoelectron spectroscopy to probe surface chemistry, and electrochemical measurements such as linear sweep voltammetry, cyclic voltammetry, and electrochemical impedance spectroscopy—the researchers showed that nickel doping does not simply add a second catalytic site. Instead, it modulates the electronic structure of the copper itself. Nickel atoms, embedded within the copper lattice or in close bimetallic proximity, shift the electron density around copper atoms in ways that stabilize the Cu+ oxidation state at the catalyst surface. That stabilization matters because Cu+ species are widely believed to be key active sites for carbon-carbon coupling; plain copper surfaces tend to lose Cu+ to metallic Cu0 under working conditions, which favors single-carbon products and hydrogen evolution instead.

The second consequence of this electronic tuning is an enriched surface coverage of adsorbed carbon monoxide, the CO intermediate, on the catalyst surface. In the generally accepted mechanism of carbon dioxide electroreduction on copper, carbon dioxide is first converted to CO, and two neighboring CO species must then couple to form a OCCO dimer, the critical carbon-carbon bond-forming step on the road to ethylene. The rate of that coupling depends on both the thermodynamic tendency of CO species to bind to the surface and their local concentration. By stabilizing Cu+ sites and tuning the binding energy of CO, nickel doping raises the surface CO coverage, bringing neighboring intermediates close enough to dimerize efficiently. At the same time, the doping adjusts the CO binding strength into a favorable window: if *CO binds too weakly it desorbs as carbon monoxide gas before coupling, and if it binds too strongly it poisons the surface. The nickel-modified copper appears to sit near the optimum of this balance, which explains the shift in selectivity from single-carbon products toward ethylene.

The porous architecture inherited from the MOF template provides a complementary advantage. Because the calcined catalyst retains an open, hierarchical pore network, carbon dioxide can diffuse rapidly to active sites and the gaseous products can escape, improving mass transport at high current densities. Just as importantly, the confined pore spaces act as nanoscale reactors that trap reactive intermediates near one another, effectively raising their local concentration and further promoting the carbon-carbon coupling step. This dual function—facilitating transport while confining intermediates—illustrates why MOF-derived catalysts have attracted such intense interest: the template strategy decouples, to some degree, the need for high surface area from the need for a specific surface chemistry, allowing both to be engineered simultaneously. The team’s systematic comparison across the series of nickel loadings showed that selectivity for multi-carbon products peaked at an intermediate composition, consistent with the picture of an optimal electronic and structural balance rather than a simple monotonic effect.

The broader context makes the result timely. Ethylene is the world’s most produced organic chemical, serving as the feedstock for polyethylene and countless other polymers, and it is currently made almost exclusively from petroleum cracking at high temperatures. A route that converts carbon dioxide into ethylene using renewable electricity would simultaneously recycle a greenhouse gas and displace a fossil-intensive process. The obstacle has always been economics: electrosynthesis of ethylene must compete with petrochemical prices, which demands high selectivity, high current density, and long catalyst lifetimes all at once. Recent years have seen rapid progress on copper catalysts—oxide-derived copper, grain-engineered foils, molecular additives, and tandem catalysts—but each strategy carries trade-offs in cost, scalability, or stability. The bimetallic electronic modulation strategy demonstrated here, in which a cheap and earth-abundant dopant (nickel) tunes an abundant host (copper) within a scalable MOF-templated synthesis, offers a comparatively simple and industrially plausible route to the same goal.

The study’s diagnostic toolkit also provides a methodological template for the field. By combining X-ray photoelectron spectroscopy, which quantifies the Cu+ to Cu0 ratio at the surface, with product analysis by gas chromatography and nuclear magnetic resonance of the liquid phase, the researchers could correlate the oxidation-state balance with Faradaic efficiencies across the catalyst series. Electrochemical impedance spectroscopy revealed reduced charge-transfer resistance for the optimized sample, indicating that the bimetallic surface not only changes chemistry but also accelerates electron transfer to the adsorbed intermediates. Linear sweep voltammetry showed the onset of carbon dioxide reduction at more positive potentials for the nickel-doped catalyst, pointing to lowered activation barriers for the rate-determining steps. Taken together, the data build a coherent mechanistic narrative in which electronic structure, intermediate coverage, and pore architecture act in concert rather than in isolation.

There remain, of course, substantial hurdles between a laboratory cell and a commercial reactor. The reported Faradaic efficiency of 55.56 percent for multi-carbon products, while impressive, still leaves nearly half of the current consumed by hydrogen evolution and single-carbon byproducts, and industrial deployment would require pushing combined selectivity and current density considerably higher while maintaining stability over thousands of hours. The experiments were conducted under the well-controlled conditions of a standard three-electrode or flow-type electrochemical setup, and real devices with gas-diffusion electrodes, recycled electrolytes, and fluctuating renewable power will impose additional stresses. Nevertheless, the 40-hour durability result and the mechanistic clarity of the electronic modulation argument give the approach credibility, and the general strategy—doping a copper MOF with a second metal chosen for its electronic effect—can in principle be extended to other dopants, other frameworks, and other target products such as ethanol, acetate, or propanol.

The work was supported by the National Natural Science Foundation of China under grant 52271356, and the authors report no competing interests. For a field racing to turn waste carbon dioxide into the building blocks of modern industry, the Dalian Maritime University and Harbin Engineering University team has contributed a conceptually clean demonstration: that the selectivity of copper is not fixed destiny but a tunable property, adjustable one electron at a time through a carefully chosen atomic neighbor. If subsequent studies can translate this bimetallic MOF-derived platform to industrially relevant current densities, the humble pairing of copper and nickel inside a porous framework may prove to be one of the more consequential recipes in the emerging toolbox of carbon-neutral chemical manufacturing.

A breakthrough led by Professor Lei Ge and his team at China University of Petroleum Beijing heralds a new era of photocatalytic CO2 conversion technologies. The group developed a zinc-doped CuInS2 (copper indium sulfide) photocatalyst, referred to as Zn-CIS, that exploits defect engineering in tandem with dual-site catalysis to dramatically enhance the efficiency of CO2 reduction into ethylene. Published in the Chinese Journal of Catalysis, this work intricately unravels the synergy between atomic-scale defects and orbital interactions that enable superior catalytic performance under visible light irradiation.

Central to the Zn-CIS catalyst’s effectiveness is the strategic incorporation of zinc ions into the CuInS2 lattice. Structural analyses complemented by theoretical computations reveal that Zn2+ ions preferentially substitute In3+ within the crystal matrix. Such doping induces an intrinsic charge imbalance that triggers the formation of sulfur vacancies, a type of defect where sulfur atoms are missing from their lattice sites. These vacancies are not mere imperfections; they fundamentally alter the electronic landscape of the material and serve crucial functions in charge dynamics.

Specifically, the sulfur vacancies act as shallow donor defects, facilitating improved separation and transport of photoexcited charge carriers. This alleviation of charge recombination is instrumental in maintaining a high population of active electrons available for CO2 reduction. Moreover, these vacancies redistribute electrons toward the nearby zinc centers, thereby enriching the electronic density around Zn sites. This electron-rich environment is conducive to activating the otherwise inert CO2 molecules, priming them for the subsequent chemical transformations.

Perhaps the most fascinating aspect of Zn-CIS lies in the creation of cooperative Cu–Zn dual active sites. These neighboring metal centers operate in concert to asymmetrically adsorb CO2—where the copper atom coordinates with the carbon atom of CO2 (Cu–C interaction), and the zinc interacts with one of the oxygen atoms (Zn–O interaction). This dual-point binding bends the rigid, linear CO2 molecule, weakening its carbon-oxygen bonds and rendering it far more reactive. Importantly, the proximity of the Cu and Zn sites facilitates the crucial C–C coupling by minimizing the spatial gap between intermediates, promoting the formation of pivotal species like *COCHO that direct the reaction pathway toward ethylene.

In-depth in situ infrared spectroscopy provides experimental validation for the proposed mechanistic pathway, evidencing sequential transformations from CO2 to COOH, then CO, CHO, COCHO, and eventually to C2H4 (ethylene). Complementary density functional theory (DFT) calculations elucidate the electronic orchestration behind this progression. At the molecular orbital level, Cu 3d orbitals hybridize with the 2π antibonding orbitals of CO2, facilitating electron injection that weakens the C–O bonds. Simultaneously, electron redistribution induced by sulfur vacancies activates Zn 3d orbitals which stabilize the bent CO2 adsorption geometry, anchoring the molecule in a configuration favorable for activation and subsequent coupling.

This intricate “Cu-site electron injection coupled with Zn-site configuration anchoring” mechanism embodies a novel paradigm in catalyst design, demonstrating how tailoring electronic orbitals via dopants and defects can optimize molecular interactions at active sites. The profound understanding gained here sets the stage for designing next-generation photocatalysts with enhanced activity and selectivity toward multi-electron, multi-proton reactions that have traditionally been elusive in sustainable chemistry.

Performance testing of the optimized Zn-CIS photocatalyst under visible light illumination shows a remarkable ethylene production rate of 15.9 micromoles per gram per hour, a 5.9-fold enhancement compared to undoped CuInS2. Beyond sheer activity, the catalyst exhibits excellent electron selectivity toward ethylene formation, reaching 77.5%, a benchmark underscoring the selective, rather than indiscriminate, reduction of CO2. Stability tests demonstrate the material’s robustness, maintaining performance over extended cycles, while isotope labeling confirms that the carbon atoms in ethylene indeed originate from CO2, ruling out artifacts from other carbon sources.

This elegant work encapsulates the power of atomic precision in catalyst engineering, merging dopant-induced defects with synergistic dual-site catalysis to overcome the kinetic and thermodynamic barriers of CO2 reduction. The implications extend well beyond ethylene synthesis; the conceptual framework offers broad utility for designing photocatalysts targeting a variety of C2 and higher carbon products, pivotal for ushering in a carbon-neutral chemical economy fueled by sunlight.

Publishing in the reputable Chinese Journal of Catalysis, a leading venue recognized for cutting-edge research with a high impact factor, the research reflects the forefront of applied catalysis innovation. The collaboration between experimental characterization and theoretical simulations exemplifies modern multidisciplinary approaches necessary for tackling grand challenges in sustainable energy and catalysis.

Looking forward, the lessons learned here open avenues for exploring other tailored dopant-defect combinations and dual-site configurations beyond Zn–Cu systems, potentially broadening the scope of photocatalytic CO2 conversion products. With global carbon emissions continuing to rise, harnessing such advances to develop scalable, efficient, and selective photocatalysts can contribute significantly to a greener, circular carbon society.

Through this pioneering research, Professor Lei Ge’s team not only advances the fundamental science of CO2 photocatalysis but also moves the needle closer to practical applications where sunlight drives valuable fuel and chemical production from waste carbon, directly addressing the urgent climate imperatives of our era.

Subject of Research: Photocatalytic CO2 reduction to ethylene using defect-engineered zinc-doped CuInS2 catalysts.

Article Title: Defect-mediated dual-site synergy in Zn-CuInS2 enables orbital-tailored high performance photocatalytic CO2-to-ethylene conversion

News Publication Date: 11-Jun-2026

Web References: https://www.sciencedirect.com/science/article/abs/pii/S187220672665022X

References: DOI: 10.1016/S1872-2067(26)65022-X

Image Credits: Chinese Journal of Catalysis

Keywords

Photocatalysis, CO2 reduction, ethylene production, CuInS2, zinc doping, sulfur vacancies, dual-site catalysis, orbital interaction, charge redistribution, defect engineering, density functional theory, green chemistry