Nonmetallic Heteroatom Engineering in Copper-Based Electrocatalysts: Advances in CO₂ Reduction

Abstract

With the escalating challenges of global warming and the energy crisis, electrocatalytic CO₂ reduction reaction (CO₂RR) has emerged as a promising strategy to mitigate atmospheric CO₂ concentrations while converting it into high-value-added chemicals. Among various CO₂RR catalysts, copper-based materials exhibit unique capabilities for C-C coupling, yet their practical application remains constrained by several limitations: Low selectivity for C₂₊ products (typically <60%); Catalyst instability due to dynamic reconfiguration of active sites under high overpotentials; poor energy efficiency caused by competing hydrogen evolution reactions (HERs), etc. Recent studies demonstrate that nonmetallic heteroatom doping or functionalized ligand incorporation can effectively modulate the electronic structure and surface microenvironment of Cu-based catalysts, thereby enhancing CO₂RR performance. In this review, we comprehensively summarize recent advances in such strategies. We first systematically elucidate the unique advantages of copper-based catalysts as benchmark materials for multi-carbon (C₂₊) product synthesis, along with the current challenges they face. Subsequently, we highlight recent advances in modulating copper-based catalysts through the incorporation of diverse nonmetallic heteroatoms (e.g., N, S, B, P, halogens) or the introduction of functionalized ligands, with a particular focus on mechanistic insights and characterization methods aimed at enhancing C-C coupling efficiency and improving C₂₊ product selectivity. Finally, we present perspectives on the remaining opportunities and challenges in this research field.

1. Introduction

Electrocatalytic CO₂ reduction reaction (CO₂RR) has emerged as a pivotal technological pathway for the storage of renewable electricity, owing to its ability to convert CO₂ into high-value carbon-based fuels such as ethylene, ethanol, and propanol [1,2,3]. Compared with conventional carbon capture and storage (CCS), CO₂RR not only directly mitigates the greenhouse effect but also enables the closed-loop utilization of carbon retem [4,5,6].

In the research field of CO₂RR catalysts, all major material systems encounter notable performance bottlenecks. Noble metal catalysts (such as Au and Ag) exhibit outstanding catalytic activity, yet their industrial scalability is severely limited by high costs and scarce natural reserves [7,8]. Transition-metal oxides (e.g., In₂O₃, TiO₂) generally suffer from insufficient current density and poor long-term stability [9,10]. Emerging two-dimensional materials (such as Cu₂Te and MXenes) are restricted by surface chemical inertness and structural stability issues [11,12]. Single-atom catalysts (e.g., Fe-N-C, Co-N-C) demonstrate excellent CO selectivity (>90%) under laboratory conditions; however, their intricate synthesis processes (high-temperature pyrolysis and acid leaching) and stringent stability requirements (prevention of metal atom agglomeration) render them incapable of meeting the rigorous cost and durability demands of industrial-scale production [13].

Due to their distinctive catalytic characteristics, copper-based catalysts have emerged as a focal point in the investigation of CO₂RR. They are capable of significantly improving product selectivity, facilitating the formation of a wide range of high-value products such as CO, CH₄, C₂H₄, and C₂H₅OH, which are of considerable interest for sustainable energy and chemical production [14,15,16,17,18,19,20,21,22,23,24]. Compared to other metallic catalysts, Cu-based materials exhibit unparalleled capabilities in facilitating C-C coupling, primarily attributed to their specific d-orbital electronic characteristics that can effectively stabilize the key *CO intermediate [25], thereby facilitating C-C bond formation [26]. Experimental studies have demonstrated that precise surface engineering strategies—such as the control of crystal facet exposure and the construction of surface defects—can boost the selectivity toward C₂₊ products to over 60% [27,28]. Furthermore, the high natural abundance of copper in the Earth’s crust and its low raw material cost offer critical support for large-scale industrial implementation [29,30]. These combined advantages establish Cu-based catalysts as the sole catalytic system currently capable of efficiently generating multi-carbon products in CO₂RR research [6].

However, copper-based catalysts for CO₂RR still face significant challenges in performance optimization. First, the intrinsic electronic structure of copper results in a “volcano-type” distribution of adsorption energies for key intermediates (e.g., *CO, *OCCO), severely limiting the selectivity for C₂₊ products (typically <80%) [31]. Second, under reductive potentials, the surface of copper catalysts undergoes dynamic reconstruction (e.g., via oxide-derived processes). Such uncontrolled structural evolution compromises the retention of active crystal facets and metastable sites, thereby resulting in an intrinsic incompatibility between catalytic activity and durability [32]. Third, the CO₂RR process involves up to eighteen coupled electron–proton transfer steps, where intense competition between the HER and carbon chain growth pathways (C₁ vs. C₂₊) markedly lowers the overall energy efficiency. The synergistic effects of these factors result in a significant decline in C₂₊ selectivity under industrial-scale current densities (>300 mA cm⁻²), representing a critical bottleneck for large-scale implementation.

Various strategies have been successfully developed to fabricate efficient copper-based catalysts with enhanced selectivity and stability toward C₂₊ products, including structural engineering, alloying, coordination environment modulation, surface functionalization, and elemental doping [33,34,35]. Extensive literature evidence suggests nonmetal-element-modified metal catalysts have emerged as one of the most promising candidates for achieving high CO₂RR performance [36]. Compared with metal-element modification, nonmetal modification—owing to the higher electronegativity of nonmetal species—exhibits superior tunability in enhancing CO₂RR activity, selectivity, and stability. However, a comprehensive understanding of nonmetal-element-modified Cu catalysts for the CO₂RR remains lacking, which has severely hindered progress in this research field. In this review, we provide a systematic summary of recent advances in incorporating various nonmetallic heteroatoms into Cu-based catalysts for the electrochemical production of multi-carbon products. We then elaborate on the specific mechanisms by which nonmetallic heteroatom doping strategies—such as N, S, B, P, and halogens—precisely modulate the electronic structure of copper-based catalysts, stabilize catalyst–electrolyte interfaces, and optimize reaction pathways. In addition, we discuss the considerable potential of nonmetallic heteroatom-functionalized ligands in fine-tuning the electronic environment and spatial configuration of copper active sites, thereby enhancing C-C coupling capability and product selectivity. Finally, we outline future research directions and persistent challenges in the field, offering insights to advance CO₂ electroreduction technology toward higher efficiency, stability, and cost-effectiveness.

2. Nonmetallic Heteroatom Doping

Nonmetal element doping can break the structural symmetry of Cu active sites, thereby enabling precise modulation of their electronic structure and optimizing the adsorption strength of key reaction intermediates (e.g., *COOH, *CO, *OCCO). This significantly enhances both CO₂ electroreduction activity and product selectivity. Theoretical calculations and experimental studies demonstrate that such electronic structure regulation reduces the energy barrier for C-C coupling or stabilizes specific intermediates, offering a novel strategy for the directional synthesis of high-value products (e.g., multi-carbon alcohols, formic acid). Recent advances in CO₂ electroreduction highlight nonmetal doping systems primarily involving N, S, B, P, and halogens.

2.1. Nitrogen (N) Doping

Nitrogen modification of copper catalysts can generally be categorized into two distinct approaches. In the first approach, nitrogen is doped into the carbon support, which can markedly enhance the interaction between the supported copper species and the support [18,37,38,39,40,41,42,43,44,45]. This serves as an effective strategy for electronic structure tuning, thereby significantly optimizing the catalytic performance. In the second approach, N is directly incorporated into the copper-based catalysts, enabling modulation of the chemical state of Cu or the introduction of vacancies. Such modifications facilitate the adsorption of *CO on the metallic sites, thus promoting C-C coupling [46,47,48,49,50,51,52,53].

Table 1. Comparative summary of CO₂ reduction performance over N-modified Cu-catalysts.

Type	Reactor Type	Electrocatalyst	Main Products	FE (%)	Potential (V vs. RHE)	Current Density (mA cm−2)	Ref.
N doping into carbon support	Flow cell	Cu-Nx	C2H4	24.8	−0.76	−25	[39]
	H-type cell	Cu-N-C	C2H5OH	31	−0.93	−22	[43]
	GDE	Cu-N-C	C2H5OH	55	−1.2	−100	[44]
	Flow cell	R-SWCNTs	C2+	66.2	−1.08	−270	[45]
	H-type cell	Cu-SA/NPC	CH3COCH3	36.7	−0.5	−1	[40]
	H-type cell	Cu2-CuN3	C2H5OH	51	−1.1	−14.4	[41]
	GDE	Cu–Nx	C2+	73.7	−1.15	−1100	[42]
N doping into Cu-based catalyst	GDE	OMIm-Cu2O	C2+	63.3	−0.5	−600	[48]
	H-type cell	MAF-2	C2H4	51.2	−1.3	−12	[49]
	H-type cell	NH2-Cu2O	C2H4	18	−0.9	−10	[50]
	Flow cell	C3	n-propanol	54	−0.53	−300	[51]
	Flow cell	Cuδ+NCN	C2H4	77.7	−1.6	−77.7	[52]
	Flow cell	Cu@PyILs	C2H4	31.88	−1.15	−188	[53]

Note: RHE refers to the reversible hydrogen electrode.

summarizes the CO₂RR performance of representative N-modified Cu catalysts reported in the literature.

2.1.1. N Doping into Carbon Support

By introducing diverse N configurations (e.g., pyridinic and graphitic N) into the carbon framework [54], N doping disrupts the intrinsic electronic uniformity of an ideal sp² carbon lattice [55], thereby markedly modulating the local density of states and charge distribution of the carbon support and creating a polarity-enhanced, electronically tunable surface microenvironment. Meanwhile, it induces the formation of defect sites such as edges and vacancies, which provide strongly coordinating anchoring sites for metal species. Thereby influencing the local electronic structure and coordination environment of the supported Cu species. This modulation governs the adsorption, reaction, and desorption behaviors of reaction intermediates, significantly enhancing both the selectivity toward multi-carbon products and the overall reaction stability.

Engineering precatalysts to regulate electron transfer and to in situ generate ultrasmall metal clusters anchored on the substrate as highly dispersed asymmetric sites represents a particularly important strategy for promoting the formation of asymmetric products. Su et al. synthesized CuO clusters supported on N-doped carbon nanosheets (Cu/N_XC) as a dispersed electrocatalyst (x = 0.14, 0.11, 0.02, 0; x denotes the mass ratio of nitrogen to carbon), achieving high CO₂RR performance in terms of stability, activity, and selectivity [41]. Characterizations including atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and soft X-ray absorption spectroscopy (XAS) indicated that N species in the samples suppress excessive aggregation of Cu atoms and maintain atomic-scale dispersion of Cu species; notably, in Cu/N_0.14C, Cu sites are coordinated exclusively with graphitic-like N. When x = 0, the Cu/C catalyst produced only trace amounts of C₂₊ products; as the N content increased, the Faradaic efficiency (FE) toward C₂₊ products rose accordingly. In particular, Cu/N_0.14C delivered an FE as high as 73% for C₂₊ products at −1.1 V (vs. RHE) (Figure 1A), with ethanol accounting for 51% FE, and maintained stable CO₂RR performance over a 10 h test (Figure 1B). Operando XAS, X-ray absorption near edge structure (XANES) simulation, and quasi-in situ XPS revealed that the reduced CuO clusters underwent reversible transformation under applied potential (Figure 1C,D). When the potential was below −1.1 V, the absorption edge position appeared between those of Cu foil and Cu₂O, indicating that the copper ions reached an average valence state of approximately +0.5. This suggests a transformation from dispersed CuO clusters to Cu₂-CuN₃ clusters (Figure 1E). The in situ generated Cu₂-CuN₃ cluster was identified as the optimal site for the electrochemical reduction of CO₂ to ethanol. Density functional theory (DFT) calculations revealed an asymmetric charge distribution between the Cu atoms within the Cu₂-CuN₃ cluster, with the predominant charge transfer occurring at the Cu-N₃ moiety. This charge asymmetry is further amplified upon CH₃* adsorption, which is proposed to account for the markedly enhanced asymmetric pathway toward ethanol formation.

For CO₂RR, carbon-based materials serve as the primary supports for single-atom catalysts [56]. Single-atom Cu catalysts anchored on Cu-N-C are attractive electrocatalysts for CO₂RR owing to their unique electronic properties and maximized atom utilization [15,57,58]. Guan and co-workers dispersed single-atom Cu species on N-doped carbon via an N-coordination strategy [39]. The presence of nitrogen enables atomic Cu to be uniformly dispersed and stably anchored within the N-doped carbon framework in the form of Cu-N_x configurations. By tuning the carbonization temperature, both the Cu doping concentration and the Cu-N_x coordination environment can be precisely regulated. At a relatively high Cu loading (4.9 mol%), the intersite distance between neighboring Cu-N_x moieties becomes sufficiently small to facilitate C-C coupling, thereby promoting C₂H₄ formation; in contrast, when the Cu content is below 2.4 mol%, the Cu-N_x sites are more spatially separated, and the catalyst preferentially yields C₁ products such as CH₄.

Surface-functionalized carbon supports can effectively tailor the coordination environment of metal centers, thereby modulating their electronic and geometric structures and tuning the catalytic properties of the active metal sites to achieve enhanced electrocatalytic performance [54]. Wang and co-workers reported a functional group–directed strategy to modify single-walled carbon nanotubes (SWCNTs) by introducing various aryl radicals and covalently grafting them onto the SWCNT framework, thereby constructing carbon materials with specific functionalities (R-SWCNTs; R = –CH₂NH₂, –CN, –CH₂COOH, –OH, –COOH) [45]. This functionalization enables Cu nanoparticles to directly anchor to the functional groups on the aryl radicals, and the resulting composites are denoted as Cu/R-SWCNT (Figure 2A). In a flow-cell electrolyzer, Cu/CH₂NH₂ exhibited an FE for C₂₊ products of 66.2% and a partial current density of −270 mA cm⁻², outperforming Cu/CN and pristine Cu/SWCNTs (Figure 2B,C). DFT calculations indicated that, compared to the electron-withdrawing cyano group, the electron-donating amine group facilitated electron transfer from the carbon support to Cu atoms, resulting in an upward shift in the Cu d-band center (Figure 2D). This shift strengthened the adsorption of *CO and its hydrogenated derivatives on the Cu surface (Figure 2E), thereby enhancing the selectivity toward C₂ products. In situ infrared and Raman spectroscopy confirmed that the increased surface coverage of the key intermediate *CHO effectively promoted the C-C coupling process.

2.1.2. N Doping into Cu-Based Catalyst

Owing to the strong Cu-N metal–nitrogen bond energy, N dopants on Cu-based catalysts exhibit relatively high stability under CO₂RR/CORR conditions. N doping can regulate the chemical states of Cu or introduce vacancies, which is beneficial for tuning *CO adsorption on metal sites to enhance C-C coupling [46,47]. For example, Niu et al. developed a facile method to synthesize a lattice-strain-stabilized N-doped Cu (LSN-Cu) catalyst by treating the CuO surface with N₂ plasma followed by an electroreduction step. This plasma treatment spontaneously introduces defect sites, compressive lattice strain, and surface N doping. XPS analysis provides in-depth insight into the local electronic structure of the LSN-Cu catalyst (Figure 3a). The surface N content was quantified to be ~4.9%, and the N 1 s binding-energy peaks at approximately 398 and 400 eV were assigned to lattice N atoms and N vacancies, respectively. DFT calculations indicate that, under compressive strain, the formation energies of oxygen vacancies (V_O) on both pristine Cu₂O/Cu and N-doped Cu₂O/Cu surfaces increase significantly. When a 4% compressive strain is applied to the model surface, the increase is most pronounced, and the V_O formation energy reaches its maximum (Figure 3b). Under these conditions, the elevated formation energy implies a stronger resistance to oxygen removal from the reactive surface, thereby helping stabilize the Cu₂O lattice and retain the N dopants. The high-frequency band (HFB) ratio of the *CO adsorption band (HFB/(HFB + low-frequency band (LFB))) is also an important indicator for evaluating *CO coverage on defect-rich nitride/oxide-derived Cu catalysts. Compared with the Cu sample, the LSN-Cu catalyst exhibits a distinctly higher HFB ratio, which is attributed to the generation of low-coordination defect sites (Figure 3c). The formation of low-coordination defect sites on the LSN-Cu surface strengthens CO binding, thereby increasing surface CO coverage. Meanwhile, the compressive-strain-stabilized N dopants enhance C-C coupling, delivering an FE of 54 ± 3% for n-propanol, a half-cell n-propanol energy efficiency (EE) of 29%, and an n-propanol partial current density of 71 ± 7 mA cm⁻² (Figure 3d).

Ampere-level current densities for C₂₊ production are rarely achieved on Cu-based catalysts, largely because the HER, which dominates at high overpotentials, suppresses CO₂RR [12,59]. Incorporation of N can in situ construct specific Cu proximal cooperative microenvironments during catalysis, thereby inhibiting *H adsorption while optimizing the adsorption of key intermediates such as *CO. Zheng and co-workers employed N-heteroatom engineering to synthesize a nanocubic Cu₃N precatalyst. Under CO₂RR conditions, electroreduction of the parent Cu₃N drives N conversion and induces in situ reconstruction of the precatalyst into an N-Cu active phase, enabling reliable ampere-level CO₂ electrolysis to C₂₊ products [42]. The catalyst achieved a C₂₊ FE of 73.7% at −1100 mA cm⁻² and exhibited a low propensity for H₂ evolution. In situ attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and in situ surface-enhanced Raman scattering (SERS) measurements confirmed that an increased *CO coverage and suppressed HER on N-Cu steer the reaction pathway toward C₂₊ formation. DFT calculations further evaluated *CO and *H adsorption at five distinct adsorption sites on the N-Cu (100) surface, revealing favorable (i.e., stronger) *CO adsorption together with an increased free energy for H adsorption. These results indicate that *CO adsorption is markedly enhanced while HER is inhibited, thereby facilitating C-C coupling and promoting CO₂-to-C₂₊ conversion.

2.2. Sulfur (S) Doping

In Cu-based electrocatalytic CO₂ reduction systems, sulfur doping—owing to its moderate electronegativity and strong coordination ability—can act as a “solid-state ligand” to form stable Cu-S motifs with Cu, thereby enabling fine regulation of active sites at both the electronic and structural levels [20,60,61,62,63,64]. Accordingly,

Table 2. Performance comparison of sulfur-doped copper-based catalysts.

Electrocatalyst	Reactor Type	Main Products	FE (%)	Potential (V vs. RHE)	Current Density (mA cm−2)	Ref.
S-HKUST 1	H-type cell	C2H4	60	−1.32	−400	[60]
Cu2S	GDE	C2H5OH	32	−0.95	−126	[63]
Cu/SNC	GDE	C2+ alcohols	59.1	−1.4	−200	[64]

summarizes the CO₂RR performance of representative S-doped Cu-based catalysts reported in the literature.

For instance, Wang and co-workers constructed sulfur-modified polycrystalline Cu and oxide-derived Cu electrodes (SM-OD-Cu) via a simple surface-impregnation method [19]. The resulting SM-OD-Cu electrode, prepared by applying sulfur modification to an OD-Cu substrate, delivered a formate FE of 58.6% at −0.75 V vs. RHE. Sulfur modification altered both the spatial distribution and morphology of Cu₂S on the electrode surface, thereby optimizing the hydrophilic microenvironment at the reaction interface and improving the electrocatalytic performance. DFT calculations further suggested that Cu₂S suppresses CO formation and the HER, while promoting H* formation; the generated H* more readily couples with HCOO* to yield formate.

Introducing vacancy defects into metallic structures can modulate the electronic structure of neighboring atoms and alter the energy barriers of key intermediates involved in rate-determining steps, thereby impacting electrocatalytic performance [65]. Copper sulfide architectures offer a viable route to generate stable surface defects and to regulate the surface vacancy density in a controllable manner [66,67]. Zhuang and co-workers systematically investigated the effect of surface defects on the thermodynamics of the adsorbed CH₂CHO intermediate by constructing three model systems [62]: a pristine Cu slab, a Cu slab containing a single-atom vacancy, and a Cu₂S-Cu core–shell model featuring surface atomic vacancies (Figure 4a). DFT calculations showed that vacancies on the Cu shell supported by a Cu₂S core increase the energy barrier along the ethylene pathway, whereas the ethanol pathway is essentially unaffected. The combined effects of subsurface S atoms and Cu-vacancy defects suppress ethylene formation, thereby shifting the selectivity toward ethanol (Figure 4b). Guided by these DFT insights, the authors synthesized a Cu₂S-Cu core–shell catalyst enriched with surface vacancies. DFT calculations indicated that, although both ethylene and ethanol formation are thermodynamically feasible, the ethylene pathway features a lower kinetic barrier. Furthermore, in an H-cell at a fixed potential of −0.95 V (vs. RHE), the distribution of C₂₊ products was compared across various Cu-based catalysts: most control Cu catalysts still favored ethylene as the dominant C₂ product, with ethanol exhibiting a lower FE than ethylene, yielding alcohol/olefin FE ratios below 1. In contrast, the Cu₂-S-Cu-V catalyst delivered a markedly higher FE for ethanol while suppressing ethylene formation, resulting in the highest alcohol/olefin ratio among all samples. This strategy proposes that synergistic multiple active sites enable end-to-end control, spanning from C-C coupling to product selectivity.

Precisely controlling the local structure of precatalysts under CO₂RR conditions to regenerate stable active sites remains a major challenge, particularly for producing C₂₊ products [68,69,70]. Metal–organic framework (MOF)–derived materials, featuring tunable size/shape, high surface area, chemical modularity, and open metal sites, are promising precatalysts that provide an atomic-level platform for integrating isolated active species. Wen and co-workers rationally constructed isolated Cu-S motifs on an HKUST-1 precatalyst via a localized sulfur-doping strategy, yielding S-HKUST-1 (Figure 5a) [60].The catalyst achieved a remarkable current density of up to 400 mA cm⁻², with an FE for ethylene reaching 57.2%, and a total FE for multi-carbon products (ethylene, ethanol, and acetic acid) as high as 88.4% (Figure 5b). To gain deeper insight into the origin of this high performance, the team employed multiple advanced operando characterization techniques, such as operando X-ray synchrotron absorption spectroscopy, confirming that the discrete Cu-S components could stabilize highly active Cu^δ+ species under CO₂ reduction conditions (Figure 5c). Furthermore, DFT calculations clarified the mechanistic role of copper-based structures with varying degrees of sulfidation (surface configurations) in the CO₂ reduction process. The computational results revealed a significant change in the interatomic distance between Cu atoms, increasing from 2.5 Å on pristine Cu surfaces to 3.9 Å in Cu₂S (Figure 5d). In the CO₂ reduction process, CO dimerization is a critical step toward forming multi-carbon products, typically requiring two CO molecules to approach and adsorb on adjacent metal atoms. DFT calculations further demonstrated that at the Cu/Cu₂S interface, the spatial separation between Cu⁰ and Cu^δ+ sites is moderate. This configuration can synergistically lower the activation barrier for the C-C coupling step, thereby effectively promoting CO dimerization and providing favorable conditions for the efficient synthesis of multi-carbon products.

2.3. Boron (B) Doping

Cu⁺ is considered crucial in determining the selectivity toward C₂₊ products during CO₂RR [71,72,73,74,75]. However, under harsh CO₂RR conditions at highly negative potentials, Cu⁺ is inevitably reduced to metallic Cu, leading to additional issues such as limited catalyst lifetime, unstable product distributions, and poorly controlled reaction pathways. Various types of strong interactions have been shown to help stabilize metal oxidation states [75,76,77,78,79,80]. The incorporation of a small quantity of boron into the lattice of transition metals results in the formation of boron-rich transition metal structures. Such surface boron arrangements markedly improve the stability of Cu⁺ species while maintaining their intrinsic catalytic activity [78]. Accordingly,

Table 3. Comparison of the CO₂RR performance of representative boron-doped Cu-based catalysts.

Electrocatalyst	Reactor Type	Main Products	FE (%)	Potential (V vs. RHE)	Current Density (mA cm−2)	Ref.
Cu(B)-2	H-type cell	C2+	79	−1	−55	[70]
B-CuO NS	H-type cell	C2+	54.78	−1.2	−16.75	[79]
B-CuO	GDE	C2+	62.1	−0.62	−125	[80]
B-Cu2O	H-type cell	C2H4	26.13	−1.2	−35	[81]
Cu2O-BN	H-type cell	C2H4	7	−1.4	−35	[82]
B-Cu HF	Flow cell	C2+	78.9	−0.91	−2400	[83]

compares the CO₂RR performance of representative B-doped Cu-based catalysts reported in the literature. Figure 6 illustrates a schematic of B doping in Cu oxides.

For example, Li introduced boron dopants into CuO and demonstrated that B-mediated regulation of the Cu-O bond and the local electronic structure stabilizes a higher density of Cu⁺/Cu^δ+ active sites during electroreduction, thereby optimizing the adsorption and coupling environment of key intermediates (e.g., *CO) and significantly enhancing the activity and selectivity for converting CO₂ to C₂₊ multicarbon products [82]. Patra, primarily using in situ/operando spectroscopic techniques, revealed that B doping alters the electroreduction-induced reconstruction behavior of CuO and the Cu⁺/Cu⁰ ratio, modulates the local electronic structure and *CO adsorption/coverage, and thus constructs an active interface more favorable for C-C coupling, leading to higher selectivity toward C₂₊ products from CO₂ reduction [80]. Yan et al. doped boron (B) into the Cu₂O lattice (Figure 7a) [81], which strengthened Cu-O hybridization and bond strength, thereby stabilizing Cu⁺ and moderately weakening *CO binding to promote C-C coupling. Benefiting from B’s low electronegativity and available empty orbitals, B doping modulated the Cu 3d-O 2p electronic structure, reduced the driving force for oxygen migration and Cu⁺ reduction, and thus ensured structural and valence-state stability under strongly cathodic bias. B-doped Cu₂O catalysts achieving remarkable stabilization of Cu⁺ active sites at high cathodic potentials and boosting C₂H₄ selectivity by 3.5-fold compared with undoped Cu₂O. The B-Cu₂O catalyst reached a maximum FE for ethylene of 26.13% at 1.2 V (Figure 7b), significantly higher than the 9.20% obtained with pristine Cu₂O (Figure 7c). After electrolysis at −1.2 V for 60 min, Cu⁺ and Cu⁰ species coexisted on the surface of the B-Cu₂O catalyst. Even after 120 min of electrolysis at −1.2 V, the catalyst still exhibited a distinct Cu⁺ characteristic peak at 918.6 eV. This revealed that the catalyst retained the structural characteristics of Cu₂O, demonstrating excellent structural stability (Figure 7d). DFT calculations indicate that hybridization between Cu 3d and O 2p orbitals is the key to Cu⁺ stabilization. This electronic structure modification decreases the binding energy of *CO (Figure 7e) while suppressing lattice oxygen evolution, thus preserving the integrity of active sites.

To further enhance the stability of Cu⁺ species, Zhou et al. synthesized hexagonal boron nitride (h-BN) nanosheet–modified cuprous oxide (Cu₂O) nanoparticles (denoted as Cu₂O-BN) (Figure 8a) [83]. The strong electronic interaction and interfacial confinement between h-BN and Cu₂O were leveraged to stabilize surface Cu⁺ species, suppress H* adsorption, and increase CO coverage as well as the selectivity toward C-C coupling. Compared with the control Cu₂O catalyst, Cu₂O-BN exhibited an increased C₂H₄ selectivity, rising from 12% to 17% (Figure 8b,c), and sustained C₂H₄ production was achieved for up to 14 h under continuous electrolysis (Figure 8d). DFT analysis indicates that h-BN modification lowers the free-energy barriers along the CO₂RR pathway (Figure 8e), accelerating the reaction while preserving product selectivity.

Wu et al. developed a hollow-fiber penetration electrode (HF) featuring high electrode/system stability, reduced ohmic losses, and improved structural robustness, enabling the eCO₂RR to readily reach ampere-level current densities [84,85,86,87]. In their recent work, they adopted a boron-doped Cu HF strategy to fabricate a B-Cu HF catalyst, achieving ampere-level CO₂-to-ethanol conversion [83]. For B-Cu HF, pre-reduction in NaBH₄ solution introduced boron dopants, and a subsequent two-step treatment—chemical reduction followed by H₂ annealing—further tuned the electronic structure of copper. In contrast, H-Cu HF was prepared by directly reducing CuO in a H₂/Ar atmosphere, yielding undoped hollow-fiber copper (Figure 9a). Cu K-edge XANES analysis revealed that the absorption edge of B-Cu HF lies between that of metallic copper (Cu⁰) and cuprous oxide (Cu₂O, Cu⁺), indicating that the Cu species are in an intermediate oxidation state (Cu^δ+, 0 < δ < +1). By comparison, the Cu valence state in the reference H-Cu HF sample is closer to metallic Cu⁰ (Figure 9b). FT-EXAFS measurements further compared the local structures of B-doped copper, electrochemically treated copper, metallic copper, and cuprous oxide. The results show that B doping substantially perturbs the Cu coordination environment, reducing the Cu-Cu coordination number (B-Cu HF: 4.9 vs. reference Cu: 12.0) and inducing lattice distortion, which increases the Cu-Cu distance (from 2.53 Å to 2.54 Å) (Figure 9c). This dual effect—altering the Cu valence state while decreasing the coordination number—not only enhances the adsorption and accumulation of locally asymmetric CO and CHO intermediates but also promotes asymmetric C-C coupling pathways. The B-Cu HPE achieved an FE of 52.4% for CO₂-to-ethanol conversion and maintained stable operation for 150 h in 3.0 M KCl at an ultrahigh ethanol partial current density of 1.25 A cm⁻². The corresponding ethanol production rate reached 3.87 mmol cm⁻² h⁻¹, together with a C₂₊ FE of 78.9% and a total current density of 2.4 A cm⁻². As a result, under an optimal current density of 2.4 A cm⁻² sustained over 150 h, the FE for C₂₊ products reached a maximum of 78.9% (Figure 9d).

2.4. Phosphorus (P) Doping

Phosphorus (P) doping represents an important non-metal strategy for tuning the performance of Cu-based catalysts, offering both electronic structure modulation and surface chemical modification. Owing to its high electronegativity and strong bonding capability, P atoms can form Cu-P coordination structures on the copper surface or partially substitute oxygen atoms in the lattice. These interactions markedly shift the d-band center and alter the local charge distribution of the catalyst [21,88,89,90,91,92], stabilizing *CO and active H₂O [93,94,95]. Schematic illustration of P doping in metallic Cu catalysts as shown in Figure 10.

Table 4. Comparison of the CO₂RR performance of representative phosphorus-doped Cu-based catalysts.

Electrocatalyst	Reactor Type	Main Products	FE (%)	Potential (V vs. RHE)	Current Density (mA cm−2)	Ref.
SCB/NG	Flow-cell	C2+	92.4	−1.8	−50	[62]
P-Cu	H-type cell	C2+	80.2	−1.2	−40.4	[93]
Cu-P	H-type cell	C2+	53.5	−1.15	−16	[94]
Cu0.92P0.08	Flow-cell	C2+	64	−2	−210	[95]

compares the CO₂RR performance of representative phosphorus-doped Cu-based catalysts reported in the literature.

Li et al. tailored the surface chemical composition of copper-plated electrodes to introduce phosphorus species [94]. The resulting Cu-P electrodes exhibited stronger CO adsorption capability and dramatically reduced the activation barrier for CO dimerization (C-C coupling) to approximately 0.25 eV, achieving FE for C₂₊ products (ethylene and ethanol) exceeding 50%, nearly twice that of conventional polycrystalline Cu. In situ Raman spectroscopy combined with DFT calculations further revealed that P doping introduces surface defect sites and optimizes local proton concentration, effectively promoting multi-carbon product formation while suppressing C₁ product generation.

Kong and co-workers synthesized a high-phosphorus-content catalyst, via a gas-phase phosphidation method using NaH₂PO₄·H₂O as the phosphorus source [95]. In this process, a copper substrate was treated at 400 °C under N₂, followed by gradient tuning of the reduction temperature in H₂ (400 °C or 600 °C) to adjust the phosphorus doping level. These samples are denoted as Cu, Cu_0.95P_0.05, Cu_0.92P_0.08, and Cu_0.90P_0.10, respectively. Incorporation of phosphorus effectively stabilized the oxidation state of copper (Cu^δ+) and significantly modulated the CO adsorption strength. XPS analysis revealed that, as the P/Cu molar ratio increased from 0 to 0.10, the d-band center of copper shifted from 4.22 eV toward the Fermi level to 3.58 eV (Figure 11a), indicating a substantial enhancement in electronic interactions between the catalyst surface and adsorbates. This electronic effect directly strengthened the chemisorption of CO, thereby optimizing the C-C coupling pathway. Electrochemical performance tests showed that at a phosphorus doping level of 8.3%, the catalyst achieved an FE of 64% for C₂₊ products at a current density of 210 mA cm⁻². Further optimization to a Cu_0.92P_0.08 composition increased the partial current density for C₂₊ products to a peak value of 176 mA cm⁻² under a total current density of 300 mA cm⁻², representing a nearly 1.9-fold improvement over undoped copper (Figure 11b). Both theoretical calculations and experimental results confirm that this optimized electronic structure provides CO adsorption on the Cu-P catalyst surface of ideal strength: strong enough to ensure sufficient CO coverage and overcome the limitations of weak adsorption, yet moderate enough to avoid excessive site blocking that can result from overly strong adsorption.

2.5. Halogen Doping

Halogen elements (X = F, Cl, Br, I), characterized by high electronegativity and strong coordination ability, can form stable Cu-X chemical bonds on the copper surface, thereby enabling dual regulation of catalytic performance through both electronic and geometric effects. Halogen-modified Cu-based catalysts not only optimize the adsorption strength of CO intermediates and lower the reaction energy barrier of C-C coupling but also induce surface dynamic reconstruction to form stable Cu⁺ active sites. These effects markedly enhance the selectivity and reaction kinetics toward C₂₊ products in CO₂RR [96,97,98,99,100,101,102,103,104]. Accordingly,

Table 5. CO₂RR performance of representative halogen (X = F, Cl, Br, I)–modified Cu-based catalysts.

Electrocatalyst	Reactor Type	Main Products	FE (%)	Potential (V vs. RHE)	Current Density (mA cm−2)	Ref.
Cu3-X	GDE	C2H4	55.01	−1.05	−15	[99]
Cu-PzH	Flow cell	C2H4	60	−1	−346.46	[100]
Cu-PzI	Flow cell	CH4	52	−0.9	−287.52	[100]
F-Cu	GDE	C2+	80	−0.8	−1600	[101]
Cu-Cl	GDE	C2H5OH	26.2	−0.74	−343.2	[103]
Cu-CuI	GDE	C2+	71	−1	−550	[104]
Cu-F	GDE	C2+	70.4	−1.1	−400	[102]
Cu4(OH)6FCl	H-cell	C2+	53.8	−1	−15	[105]

summarizes the CO₂RR performance of representative halogen (X = F, Cl, Br, I)–modified Cu-based catalysts reported in the literature.

The halogen-modified copper catalysts (X-Cu) exhibit variations in catalyst morphology, halide content, and electrochemically active surface area (ECSA), which makes it challenging to elucidate the intrinsic role of surface halide species [106]. Ma and co-workers innovatively proposed a hydrogen-assisted C-C coupling pathway [101]. Fluorine modification promotes H₂O dissociation, and the hydrogenation of *CO to *CHO becomes the rate-determining step on the F-Cu catalyst. In addition, fluorine enhances CO adsorption by increasing the density of surface Cu^δ+ sites, thereby promoting C-C coupling. They synthesized a Cu(OH)F precursor via a solvothermal method and subsequently prepared a fluorine-modified Cu catalyst (Cu(OH)F) by electrochemical reduction. They further investigated anion-exchange reactions between Cu(OH)F and ammonium halides (NH₄Cl, NH₄Br, or NH₄I), followed by electrochemical reduction to yield halogen-modified Cu catalysts denoted as X-Cu (X = Cl, Br, I). The X-Cu series catalysts exhibit similar morphology, halogen content, and ECSA, providing an appropriate model system for elucidating the role of surface halides in CO₂RR toward C₂₊ compounds. Among these, F-Cu exhibited the highest catalytic performance, achieving an FE of 80% for multi-carbon (C₂₊) products under a high current density of 1.6 A cm⁻² (Figure 12a). This group innovatively proposed a hydrogen-mediated C-C coupling pathway and conducted H/D kinetic isotope effect (KIE) tests on different X-Cu catalysts. The measured KIE values were 2.0, 1.8, 1.5, 1.3, and 1.2 for Cu, I-Cu, Br-Cu, Cl-Cu, and F-Cu, respectively. The KIE on the F-Cu catalyst decreased to nearly unity, indicating that H₂O dissociation is no longer the rate-determining step on this catalyst. Therefore, the presence of F- on Cu accelerates H₂O activation. DFT calculations revealed that halogen modification progressively reduces the energy barrier for H₂O activation, with fluorine showing the most pronounced effect—effectively lowering the barrier for water molecule dissociation so that H₂O activation no longer serves as the rate-limiting step, thereby accelerating C₂H₄ production. In situ ATR-FTIR spectra showed a distinct absorption peak at 1754 cm⁻¹, conclusively confirming the presence of chemically adsorbed CHO intermediates on the F-Cu catalyst surface. In contrast, no such spectral feature was detected on unmodified copper catalysts. Mechanistic DFT studies further revealed that fluorine doping significantly strengthens CO intermediate adsorption and promotes its hydrogenation to CHO species, thereby providing a key driving force for subsequent C-C coupling steps (Figure 12b).

Yan et al. incorporated NH₄F into a copper precursor (CuCl₂), and after co-reduction and annealing, obtained particles predominantly composed of CuO, with fluorine uniformly distributed across the particle surface [102]. Fluorine atoms modulate the local electronic structure of Cu and the CO adsorption environment (Figure 12c). Specifically, F doping facilitates interfacial electron transfer on F-Cu. Moreover, grain boundaries formed on F-Cu provide a local microenvironment that stabilizes *CO intermediates and promotes subsequent C-C coupling steps. In addition, fluorine incorporation increases the hydrophobicity of F-Cu, a change that is generally beneficial for suppressing the competing HER. This fluorine-doping strategy yielded a high-performance Cu-based catalyst capable of efficiently producing C₂₊ products under industrial-level current densities (>400 mA cm⁻²), achieving an FE of 70.4%. No appreciable performance degradation was observed during a continuous 12 h stability test (Figure 12d). In situ SERS combined with electrochemical performance analysis revealed that CO₂ can be reduced to CO at relatively low potentials (Figure 12e), a process that facilitates subsequent C-C coupling steps and promotes the formation of C₂₊ products.

The Cu⁰/Cu⁺ interfacial sites in partially oxidized Cu matrices are conducive to CO₂ activation and the subsequent C-C coupling [107]. Accordingly, halide-modification strategies are regarded as an effective means to tune the activity and selectivity of Cu catalysts [101]. Li and co-workers designed a Cu-CuI composite catalyst featuring abundant Cu⁰/Cu⁺ interfacial sites by physically mixing copper nanoparticles with copper (I) iodide (CuI) powder [104]. In a flow cell, the composite catalyst achieved a maximum FE of 71% toward C₂₊ products, with a partial current density for C₂₊ of 591 mA cm⁻² at −1.0 V vs. RHE—significantly higher than that of either Cu or CuI alone (Figure 13a,b). At −0.8 V vs. RHE, the catalyst maintained a geometric current density of ~550 mA cm⁻² over 85 h, with only a slight decrease in the FE for ethylene and overall C₂₊ products (Figure 13c). DFT calculations revealed that surface-reconstructed Cu⁺ species and adsorbed iodine atoms are the primary contributors to the high C₂₊ selectivity observed with the Cu-CuI composite catalyst. The adsorbed iodine species play a dual role: stabilizing Cu⁺ species to enhance C-C coupling and directly promoting C-C coupling by modulating the adsorption strength of CO intermediates (Figure 13d).

Furthermore, Yang’s team designed a novel halogen-containing catalyst precursor, Cu₄(OH)₆FCl nanosheets (Figure 14a) [105]. Upon activation under the reaction conditions, the precursor was transformed into a porous Cu catalyst. Detailed post-reaction analyses of the catalyst deposited on the electrode revealed that the activated material exhibited a sheet-like porous metallic copper structure composed of Cu crystallites. XPS confirm that the residual Cl atoms in porous metallic Cu can induce the formation of stable mixed-valence Cu species (Figure 14b). During the process, the F element showed instability (Figure 14c) and gradually leached out as the reaction proceeded. In contrast, Cl atoms remained stably incorporated in the activated Cu catalyst throughout the reaction (Figure 14d). Together with the preserved sheet-like porous morphology during operation, this stability endowed the catalyst with high C₂₊ selectivity and excellent durability. Even after 240 h of continuous electrolysis, the catalyst maintained a high C₂₊ selectivity (Figure 14e). Under optimal conditions, the Faradaic efficiency and partial current density for C₂₊ products reached 53.8% and 15.0 mA·cm⁻², respectively.

3. Nonmetal-Heteroatom-Functionalized Ligands

In CO₂RR, the arrangement of surface atoms and the electronic structure of the catalyst are critical determinants of reaction selectivity and energy efficiency [76,108,109]. In recent years, researchers have proposed a strategy of introducing nonmetal-heteroatom-functionalized ligands onto the surface of Cu-based catalysts. Through targeted chemical modification, this approach enables precise tuning of both the electronic environment and spatial configuration of the active sites, thereby modulating the adsorption behavior and conversion pathways of reaction intermediates [110,111]. Distinct from conventional metal-centered modulation, functionalized ligands can coordinate directly to metal centers, incorporating heteroatoms with specific electronic attributes (such as N, F, Cl, and O). These heteroatoms can regulate the metal’s electron density and chemical reactivity via electron-donating or electron-withdrawing effects, while synergistically enhancing selectivity and stability through steric hindrance, modulation of the local surface microenvironment, and stabilization of key intermediates [112].

Yang et al. constructed a class of structurally stable copper coordination polymers (Cu-CPs) by self-assembling copper salts with meticulously designed organic ligands (Figure 15a) under either solution-phase or hydrothermal conditions [113]. The Cu coordination environment and oxidation state can be precisely regulated via ligand electronic and steric effects, thereby optimizing the d-band position and Lewis acidity to stabilize co-adsorbed *CO intermediates and promote C-C coupling. This approach established a molecular platform enabling precise modulation of the electronic structure of the metal centers (Figure 15b,c). By systematically tuning the highest occupied molecular orbital (HOMO) energy levels of the ligands, the authors achieved broad control over the electronic states of Cu active sites, thereby markedly enhancing the C-C coupling capability of Cu-CP catalysts in the electrochemical reduction of CO₂. Electrocatalytic results revealed a pronounced dependence of product distribution on ligand structure. In particular, the L2-Cu catalyst exhibited the highest selectivity toward C₂₊ products (FE_C2+ = 77%), while effectively suppressing the formation of C₁ byproducts (Figure 15d). In situ Cu K-edge XANES analysis demonstrated that, within the potential range of −0.69 V to −0.79 V, the XANES spectra of L2-Cu remained highly consistent with those in its initial state, with no detectable signals corresponding to Cu₂₊ or metallic Cu aggregation. This observation indicates that the Cu centers persist in a low-valent state and remain stably coordinated to the ligand framework throughout the reaction (Figure 15e). To elucidate the behavior of reaction intermediates, CO desorption kinetics (time-decay method) were employed to quantitatively evaluate the *CO adsorption strength of various Ln-Cu catalysts, using the time to reach a normalized intensity of 0.5 (t_0.5) as a descriptor of desorption rate. L2-Cu exhibited the largest t_0.5 value (≈120 s), corresponding to the slowest CO desorption and therefore the strongest *CO binding (Figure 15f). By correlating t_0.5 with *CO vibrational frequencies obtained from in situ Raman spectroscopy, the authors established a relationship between *CO binding strength and η_C–C (C-C coupling efficiency parameter). The results reveal a characteristic volcano-type dependence: under moderate binding strength conditions (e.g., L2-Cu, t_0.5 ≈ 120 s, Raman shift ≈ 2030 cm⁻¹), η_C-C reaches a peak value (>0.8), whereas excessively strong or weak binding significantly reduces coupling efficiency (Figure 15g). This work quantitatively links *CO binding strength at homogeneous Cu active sites to C-C coupling efficiency, underscoring the critical role of molecular ligand engineering in optimizing metal–intermediate interactions. The authors suggest that future research could focus on synthesizing coordination polymers with broader tunability of electronic properties and intermediate adsorption energies, thereby deepening the mechanistic understanding of structure–performance relationships and enabling the development of more efficient CO₂RR catalysts.

Wu et al. proposed a strategy based on aryl diazonium salt-functionalized copper catalysts to achieve precise regulation of the C-C coupling step in the CO₂ electroreduction reaction (CO₂RR) [114]. In this method, copper catalysts are first prepared via electrodeposition on acid-treated gas diffusion electrodes (GDEs) at a current density of −15 mA cm⁻² in an electrolyte containing CuBr₂, sodium tartrate, and KOH. The obtained copper catalysts are subsequently subjected to surface chemical reactions with aryl diazonium salts bearing different substituents (Figure 16a), thereby constructing a continuous functionalization layer of approximately 5–8 nm thickness. This layer is predominantly anchored to the metallic surface through azo bonds, enabling effective modulation of the Cu valence state without substantially altering the catalyst morphology, thus facilitating the coupling of CO intermediates. Cu K-edge XANES spectra of the functionalized catalysts after electrochemical reduction reveal that distinct aryl substituents can achieve fine-tuning of the electronic structure of the copper surface. In particular, the Cu-NN catalyst exhibits an average Cu valence state of approximately +0.26, correlating with the highest FE toward ethylene—achieving 83% ethylene selectivity and a specific current density of 212 mA cm⁻² at relatively low overpotentials (Figure 16b). This catalyst maintains stable performance over 120 h of continuous operation (Figure 16c) and effectively suppresses the formation of undesired byproducts such as CH₄ and H₂. DFT calculations further elucidate the underlying mechanism of this strategy: aryl functionalization optimizes the CO adsorption energy and stabilizes key intermediates, making ethylene formation a more favorable thermodynamic pathway.

4. Conclusions and Outlook

For Cu-based catalysts, elucidating the structure–activity relationship is essential for achieving rational design. However, there is currently a lack of universal theoretical models capable of reliably predicting the impact of electronic structure modulation, and materials development still relies heavily on empirical trial-and-error and extensive experimental screening. Heteroatom incorporation can significantly alter the d-band center, Fermi level, local charge density, and surface adsorption energies of the Cu matrix, thereby influencing CO₂ activation and the reaction pathways of key intermediates such as *CO and *CHO. These effects are highly dependent on factors including the intrinsic properties of the heteroatom, doping site, doping concentration, distribution uniformity, and the dynamic surface evolution under operating conditions. Due to the complex coupling among these parameters, the same strategy may yield opposite outcomes across different systems. This highlights an urgent need for predictive, cross-system models that can rationalize heteroatom effects and guide the design of Cu-based CO₂RR catalysts.

4.1. Current Challenges and Outlook for Heteroatom-Doped Copper-Based Catalysts

The face-centered cubic lattice of copper-based catalysts exhibits high sensitivity to the incorporation site of heteroatoms such as N, S, and B, with different doping configurations—substitutional, interstitial, and surface adsorption—significantly altering the local electronic structure and catalytic performance. Conventional synthesis methods (e.g., high-temperature solid-state reaction, wet-chemical reduction) often fail to precisely control doping sites, typically resulting in random distributions that induce lattice distortion [115] and generate inactive phases such as Cu₂O, Cu₃C, and CuS. These phases decrease electrical conductivity, weaken CO₂ adsorption and *CO coupling capability, and ultimately reduce Faradaic efficiency [95]. Random doping also leads to heterogeneous active sites and inconsistent electronic structures, thereby impairing the adsorption of key intermediates (*CO, *COOH). Under CO₂RR conditions, doped atoms are prone to leaching, migration, or over-reduction, which disrupts coordination structures, triggers surface reconstruction, deteriorates reaction kinetics, and results in diminished activity and selectivity. Therefore, the development of synthetic strategies capable of precisely controlling doping positions is essential to enhance the binding energy between heteroatoms and the Cu lattice, introduce multiple coordination environments, and adjust potential and reaction conditions during operation to improve long-term stability.

4.2. Key Challenges in Heteroatom Functionalization of Ligands

Heteroatom functionalization of ligands offers a promising route to enhance the activity, selectivity, and stability of Cu-based electrocatalysts for the CO₂ reduction reaction (CO₂RR). By modulating the electronic structure and local reaction microenvironment at the catalyst surface, heteroatoms can effectively facilitate the formation and conversion of key intermediates, such as *CO and *CHO. Nevertheless, this strategy still faces multiple challenges at both theoretical and practical levels, requiring continuous advances in mechanistic understanding, materials design, and scalable synthesis.

Chemical stability represents a critical bottleneck limiting the long-term operation of Cu-based ligand catalysts. Many organic ligands and their heteroatom functional groups are prone to dissociation, degradation, or structural reconstruction under strongly reducing potentials and complex electrolytes, resulting in the deactivation of active sites. To address this, future strategies may incorporate conjugated polymers, rigid macrocyclic frameworks, or inert heteroatoms to improve resistance against reductive conditions. In terms of performance tuning, precise control over intermediate adsorption and product distribution is essential. Introducing sterically hindered architectures could modulate the spacing between Cu sites and alter binding kinetics, offering new avenues for optimizing reaction pathways. Moreover, multi-heteroatom synergistic designs—such as N/S, N/P, or O/N combinations—can integrate the benefits of electron donation, steric modulation, and proton-transfer kinetics to meet the complex requirements of the multi-step CO₂RR process, thereby achieving comprehensive improvements in catalytic stability and selectivity. For example, Hua and co-workers developed a coordination-engineering strategy to precisely tune the electronic structure of copper clusters. N doping promotes CO₂ activation, whereas S doping lowers the adsorption barrier of *CO and facilitates H₂O activation. This synergy directs an asymmetric *CO-*COH coupling pathway, thereby reducing the reaction energy barrier. Moreover, S/N co-doping precisely modulates the adsorption energies of oxygenated intermediates and induces redistribution of electron density at O sites. This weakens Cu-O bonding while strengthening C-O bonding and simultaneously suppresses competing reactions (e.g., ethylene formation), ultimately promoting alcohol production [64].