Yueguang Chen

Single‐atom catalysts (SACs) have redefined the landscape of heterogeneous catalysis by offering atom‐level precision and remarkable activity in small‐molecule transformations. Yet, their inherently isolated active centers limit the ability to mediate complex multi‐step reactions such as cascade, tandem, and multi‐intermediate conversions. To address this challenge, multi‐tiered site engineering (MTSE), a conceptual framework in which spatially and electronically coupled active sites cooperate to transcend the constraints of conventional mono‐site catalysis is introduced. MTSE advances SAC design along four key dimensions: dual‐atom ensembles, single‐atom/nanostructure hybrids, functional group cooperativity, and support‐mediated electronic modulation. By orchestrating synergistic adsorption and stepwise intermediate conversion, these strategies unlock efficient routes for CO ₂ conversion into fuels and high‐value chemicals. Progress across thermal, electrocatalytic, and photocatalytic systems, highlighting how MTSE enhances activity, selectivity, and durability through deliberate multi‐site interplay is critically assessed. Cutting‐edge in situ and operando spectroscopies are emphasized as indispensable for unraveling dynamic intermediates and structure‐function correlations. Looking forward, pressing challenges, including atomically precise synthesis, mechanistic deconvolution of cooperative pathways, and integration into cascade process design are identified. This review positions MTSE as a transformative paradigm for next‐generation SACs and a pathway toward sustainable CO ₂ valorization.

Precision engineering of intermetallic spacing and electronic synergy in heteronuclear dual‐atom catalysts (DACs) remains a pivotal challenge. Herein, the synthesis of a nitrogen‐doped hollow carbon‐supported Pd─Cu DAC is reported via a polymer‐mediated confinement strategy, achieving sub‐3 Å Pd─Cu spacing. This atomic‐scale proximity, stabilized by 2N‐bridged heteronuclear pairs, supports a charge asymmetry configuration, which enables cooperative catalysis of reactants within active pockets, thereby enhancing the Sonogashira coupling reaction performance. Specifically, electron‐rich Pd activates C─X bonds (X═I, Br, Cl) via optimized electronic structure, while electron‐deficient Cu centers stabilize alkynyl intermediates, effectively suppressing byproducts. The Pd─Cu/NC demonstrates exceptional performance, achieving high selectivity and 94% yield at a turnover frequency of 889 h⁻¹, with ultralow Pd usage (2 ppm). This significantly outperforms long‐distance Pd/Cu single‐atom catalysts (79% yield) and inactive PdCu alloys. Operando spectroscopy and theoretical calculations confirm that fast intermediate transfer between Pd─Cu sites reduces the energy barriers for C─C coupling compared to isolated Pd site systems. The active locking architectures of intimate Pd─Cu sites ensure ligand‐free operation, excellent durability, and broad substrate scope, including bromo‐/chloroarenes, which are challenging in traditional heterogeneous catalysis. This work highlights atomic‐level distance engineering as a key strategy for enhancing site cooperativity efficiency.

Single atomic sites (SAs) face challenges in catalyzing complex chemical processes involving multiple intermediates due to rigid coordination environments, steric hindrances, and limited activation behaviors. Herein, an alloying‐mediated element repartition method is developed to synthesize flexible cesium single‐atom catalysts, anchoring Cs single sites on precisely controlled amorphous‐MgO/crystalline NbC hetero‐phase nano‐supports. The amorphousMgO(a‐MgO) equipped Cs ₁ ‐a‐MgO/NbC achieves 91% yield in the cyclization of CO ₂ with 2‐aminobenzonitrile within a complex gas–liquid–solid triphasic system, outperforming its counterpart fabricated with rigid crystalline MgO, Cs ₁ ‐c‐MgO/NbC catalyst (only a yield of 23%). The Cs ₁ ‐a‐MgO/NbC shows excellent tolerance to various functional groups in sustainable catalysis, especially removing the traditional requirement for high‐pressure conditions and additives. Operando spectroscopic characterizations and theoretical calculations demonstrate that sandwich‐structural Cs ₁ ‐a‐MgO/NbC enhances the consecutive activation through vertically adsorbed configurations of intermediates during the C‐N coupling and N‐heterocyclic ring formation. Cs SAs supported by a‐MgO nano‐cushions allow for adaptability to the dynamic transformations of multiple intermediates via tensile Cs‐O and compressive Mg─O bonds, ultimately reducing the energy barriers of critical rearrangement and isomerization steps. This study provides valuable insights into designing flexible SACs to overcome the limitations of rigid support interfaces, thereby enhancing performance toward multi‐intermediate conversion in heterogeneous catalytic transformations.

Increasing the utilization efficiency of platinum is critical for advancing proton exchange-membrane fuel cells (PEMFCs). Despite extensive research on catalysts for the cathodic oxygen reduction reaction (ORR), developing highly active and durable Pt-based catalysts that can suppress surface dealloying in corrosive acid conditions remains challenging. Herein, we report a facile synthesis of bimetallic ultrathin PtM (M = Mo, W, and Cr) nanowires (NWs) composed of group VI B transition metal atomic sites anchored on the surface. These NWs possess uniform sizes and well-controlled atomic arrangements. Compared to PtW and PtCr catalysts, the PtMo_0.05 NWs exhibit the highest half-wave potential of 0.935 V and a mass activity of 1.43 A·mg_Pt⁻¹. Remarkably, they demonstrate a remarkable 23.8-fold enhancement in mass activity compared to commercial Pt/C for ORR, surpassing previously reported Pt-based catalysts. Additionally, the PtMo NWs cathode in membrane electrode assembly tests achieves a remarkable peak power density of 1.443 W·cm⁻² (H₂-O₂ conditions at 80 °C), which is 1.09 times that of commercial Pt/C. The ligand effect in the bimetallic surface not only facilitates strong coupling between Mo (4d) and Pt (5d) atomic orbitals to hinder atom leaching but also modulates the d-states of active site, significantly optimizing the adsorption of key oxygen (^⋆O and ^⋆OH) species and accelerating the rate-determining step in ORR pathways.

Fine regulation of geometric structures has great promise to acquire specific electronic structures and improve the catalytic performance of single-atom catalysts, yet it remains a challenge. Herein, a novel seed encapsulation-decomposition strategy is proposed for the geometric distortion engineering and thermal atomization of a series of Cu-N_x/S moieties anchored on carbon supports. During pyrolysis, seeds (Cu²⁺, CuO, or Cu₇S₄ nanoparticles) confined in metal organic framework can accommodate single Cu atoms with Cu—N or Cu—S coordination bonds and simultaneously induce C—S or C—N bond cleavage in the second coordination shell of Cu centers, which are identified to manipulate the distortion degree of Cu-N_x/S moieties. The severely distorted Cu-N₃S molecular structure endows the resultant catalyst with excellent oxygen reduction reaction activity (E_1/2 = 0.885 V) and zinc-air battery performance (peak power density of 210 mW·cm⁻²), outperforming the asymmetrical and symmetrical Cu-N₄ structures. A combined experimental and theoretical study reveals that the geometric distortion of Cu-N_x/S moieties creates uneven charge distribution by a unique topological correlation effect, which increases the metal charge and shifts the d-band center toward the Fermi level, thereby optimizing the inter-mediate adsorption energy.

The design of low-cost yet highly efficient electrocatalysts plays a critical role in energy storage and conversion reactions. The oxygen evolution reaction (OER) is considered a bottleneck of electrochemical water splitting for hydrogen fuel generation. It is still challenging to extract a high density of charge carriers in noble-metal-free alternative catalysts to facilitate sluggish kinetics. Herein, we report the rational design and coherent interface engineering for combining light-harvesting Cu₃₁S₁₆ with electroactive Co_9–xNi_xS₈ (x = 0–9) to form novel Cu₃₁S₁₆–Co_9–xNi_xS₈ heterodimers. By delicately controlling the kinetic growth in a seed-mediated growth method, the bifunctional centers, even with two distinct crystal phases, were integrated into a synergistic architecture, which achieved full-spectrum solar energy capture and light conversion to drive and activate the electrochemical reaction. Benefiting from the well-defined structure, high-quality interface, oriented attachment, and optimal Co/Ni bimetal ratio, Cu₃₁S₁₆–Co_7.2Ni_1.8S₈ produces a dramatically reduced overpotential (242 mV at 10 mA cm^–2) with a shift of 83 mV under visible-light excitation, achieving a 4.5-fold higher turnover frequency than that of its unirradiated Co_7.2Ni_1.8S₈ counterpart. This enhanced performance also far exceeds commercial RuO₂ (358 mV at 10 mA cm^–2) and most nonprecious-metal nanocatalysts. Further mechanistic studies reveal that coherent interface engineering leads to a strong photo/electricity coupling effect and efficient spatial charge separation, which induces sufficient hot holes that eventually accumulate at the electroactive sites to accelerate the multihole-involved OER. This work would open up new opportunities for the fabrication of non-noble metal electrocatalysts and management of charge carriers.

The crucial issue for fuel cells is to improve the activity and durability of Pt‐based catalysts. Herein, based on the short distance enhancement effects, a novel PtCo@NC catalyst with remarkably enhanced electrocatalytic properties for methanol oxidation reaction (MOR) in acidic electrolytes is developed by shortening the Pt–Co active site distance. In brief, a series of PtCo@NC catalysts with different Pt–Co biatomic arrangement are precisely synthesized by an in situ reduction‐fusion method, achieving Pt–Co structural evolution from a Pt/Co individual monometallic islet (A‐700 °C) to PtCo heterodimer (A‐800 °C) and then a PtCo alloy (A‐900 °C) embedded on nitrogen‐doped carbon matrixes. Compared with the Pt/Co monometallic islet and heterodimer, the PtCo@NC (A‐900 °C) with the shortest Pt–Co active site distance exhibits the highest mass activity of 2.30 A mg_Pt⁻¹, which is 12.23 times higher than that of commercial Pt/C and exceeds almost all the reported MOR catalysts in acidic electrolytes. Both experiments and density functional theory calculations reveal that the remarkably improved activity stems from the modification of electron distribution around Pt/Co metal centers, thus promoting the rate‐determining methanol dehydrogenation step and CO oxidative removal processes, which are dependent on the distance between bimetallic active sites.

The synergy of fully-exposed active sites and optimized N-dopant configurations in three-dimensional (3D) N-doped carbon (N/C) is highly pivotal for efficient catalysis and energy conversion but lacks effective methods. Meanwhile, to understand the active sites, excluding the size effect of the π-conjugated system, especially in N/C derived from metal-organic-frames (MOFs), is significant but challenging. Herein, an elegant and general strategy, ligand competitive thermolysis, was developed to construct hierarchical-pore structures and tailor their N-coordination environment in the MOF-derived, 3D N/C catalysts. Due to sufficient interior mesopores and predominant active-N species, the metal-free catalysts achieved efficient activity (E1/2 = 0.84 V) and impressive durability (20,000 cycles, E1/2 = 5 mV). The relationship between half-wave potential and the content of N species were also investigated. This work not only offers valuable inspiration for developing high-performance electrocatalysts, but also motivates deep understanding of the active sites in N/C catalysts.