Engineering of Coordination Environment and Multiscale Structure in Single-Site Copper Catalyst for Superior Electrocatalytic Oxygen Reduction

Herein, we report efficient single copper atom catalysts that consist of dense atomic Cu sites dispersed on a three-dimensional carbon matrix with highly enhanced mesoporous structures and improved active site accessibility (Cu-SA/NC(meso)). The ratio of +1 to +2 oxidation state of the Cu sites in the Cu-SA/NC(meso) catalysts can be controlled by varying the urea content in the adsorption precursor, and the activity for ORR increases with the addition of Cu¹⁺ sites. The optimal Cu¹⁺-SA/NC(meso)-7 catalyst with highly accessible Cu¹⁺ sites exhibits superior ORR activity in alkaline media with a half-wave potential (E_1/2) of 0.898 V vs RHE, significantly exceeding the commercial Pt/C, along with high durability and enhanced methanol tolerance. Control experiments and theoretical calculations demonstrate that the superior ORR catalytic performance of Cu¹⁺-SA/NC(meso)-7 catalyst is attributed to the atomically dispersed Cu¹⁺ sites in catalyzing the reaction and the advantage of the introduced mesoporous structure in enhancing the mass transport.

Synergistic trifunctional electrocatalysis of pyridinic nitrogen and single transition-metal atoms anchored on pyrazine-modified graphdiyne

Multifunctional catalysts that integrate high efficiency hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) catalytic activity in a single material are attractive for unitized regenerative fuel cells and overall water splitting technologies. As the best-known HER and ORR electrocatalysts, Pt and its alloys have only moderate OER activity. Ruthenium and iridium oxides exhibit the highest OER activities but not as active as Pt for HER and ORR. Here, we proposed a general principle for achieving trifunctional electrocatalysis for three reactions in a single material. Using the newly-synthesized pyrazine-modified graphdiyne (PR-GDY) as an example, we demonstrated that the synergistic effect of the pyridinic nitrogen and anchored transition-metal (TM) single atoms renders highly-efficient HER/OER/ORR trifunctional electrocatalytic activity. For the Ni-doped PR-GDY, the overpotentials for HER, OER and ORR can be respectively as low as -0.05, 0.29 and 0.38 V, which are comparable or even superior to the best-known single-functional and bi-functional precious electrocatalysts. These computational results offer not only a promising trifunctional electrocatalyst but also a strategy for the design of multifunctional electrocatalysts.

Rare-earth single atoms decorated 2D-TiO2 nanosheets for the photodegradation of gaseous O-xylene

In this work, rare-earth single atoms (La, Er) were decorated on the surface of 2D-TiO₂ nanosheets by an impregnation-calcination strategy. The formation of rare-earth single atoms was certified by AC HAADF-STEM and XAS. TiO₂ decorated with rare-earth single atoms (La₁-TiO₂ and Er₁-TiO₂) exhibited outstanding photocatalytic activity than pure 2D-TiO₂ nanosheets (2D-TiO₂) towards gas-phase degradation of O-xylene. Compared with 2D-TiO₂, the rare-earth single atoms greatly improved the adsorption capacity of O-xylene without increasing their specific surface area. This is because rare-earth single atoms provide additional adsorption sites and reduce the adsorption energy of O-xylene. In addition, the hybrid orbital formed by the combination of rare-earth single atom and oxygen atom is beneficial to the rapid transmission and separation of photo-induced electrons, thereby improving the performance of photocatalytic degradation. In addition, in-situ DRIFTS and GC-MS were used to reveal the photocatalytic oxidation mechanism. Interestingly, the results showed that the La₁-TiO₂ and Er₁-TiO₂ samples can reduce the types of intermediates and simplify the reaction route, implying that the single atoms play an important role in the modulation and thorough mineralization of intermediate products. This work shows that the rare-earth single atom decorated 2D-TiO₂ nanosheets have great potential in photocatalytic air pollution control.

Mass Production of Pt Single-Atom-Decorated Bismuth Sulfide for n-Type Environmentally Friendly Thermoelectrics

Single-atom materials are widely explored in catalysis, batteries, sensors, etc. However, limited by mass production and centimeter-scale assembly, they are rarely studied in thermoelectrics. Herein, we demonstrate a solvothermal synthesis assisted by a syringe-pump method to yield Bi₂S₃-supported Pt single-atom materials (Bi₂S₃-Pt₁) at a 10 g scale. Different from Pt_n clusters, Pt₁ single atoms can increase carrier concentration at a high doping efficiency and provide a unique atomic environment to enhance carrier mobility, and an enlarged effective mass leads to an enhanced Seebeck coefficient. As a result, a high power factor (348 μW m^-1 K^-2) is achieved at 823 K. Benefiting from the scattering of phonons by Pt₁ atomic sites, a minimum thermal conductivity of 0.37 W m^-1 K^-1 is achieved. Consequently, the Bi₂S₃-0.5 wt % Pt₁ realizes a record-high zT of ∼0.75 at 823 K, being among the best in the state-of-the-art n-type environmentally friendly metal sulfides. The enhancement of the carrier mobility and suppression of the thermal conduction by the unique Pt₁ single atoms will inspire various fields, as exemplified by electronic devices and thermal management.

Synergistic effect of Pt-Ni dual single-atoms and alloy nanoparticles as a high-efficiency electrocatalyst to minimize Pt utilization at cathode in polymer electrolyte membrane fuel cells

Pt-Ni (111) alloy nanoparticles (NPs) and atomically dispersed Pt have been shown to be the most effective catalysts for oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cells (PEMFCs) as well as less expensive compared to pure Pt NPs. To meet reaction kinetic demands and minimize the Pt utilization at cathode in PEMFCs, we propose a novel electrocatalyst composed of dual single-atoms (Pt, Ni) and Pt-Ni alloy NPs dispersed on the surface of N-doped carbon (NDC); collectively, PtNi_SA-NPS-NDC. The optimized PtNi_SA-NPS-NDC catalyst displays excellent mass activity and durability compared to commercial Pt/C. Electrocatalytic measurements show that the PtNi_SA-NPS-NDC catalyst, with a metal loading of 4.5 wt%, exhibited distinguished ORR performance (E_1/2 = 0.912 V) through a 4-electron (4e^-) pathway, which is higher than that of commercial 20 wt% Pt/C (E_1/2 = 0.857 V). The DFT simulations indicate Pt-Ni alloy NPs and PtNiN₂C₄ atomic structure are the mobile active sites for ORR catalytic activity in PtNi_SA-NPS-NDC. As a cathode catalyst in PEMFC, the Pt utilization efficiency in the PtNi_SA-NPS-NDC catalyst is 0.033 g_Pt kW^-1, which is 5.6 times higher than that of commercial Pt/C (0.185g_Pt kW^-1). Therefore, the consumption of precious metals is effectively minimized.

CO2 Photoreduction over Semiconducting 2D Materials with Supported Single Atoms: Recent Progress and Challenges

In the face of the growing energy crisis and environmental challenges, substantial efforts are now directed toward sustainable clean energy as a replacement for traditional fossil fuels. CO2 photoreduction into value-added chemicals and fuels is widely recognized as a promising approach to mitigate current energy and environmental concerns. Photocatalysts comprising single atoms (SAs) supported on two-dimensional (2D) semiconducting materials (SAs-2DSemi) have emerged as a novel frontier due to the combined merits of SA catalysts and 2D materials. In this study, we review advancements in metal SAs confined on 2DSemi substrates, categorized into four groups: (1) metal oxide-based, (2) g-C3N4-based, (3) emerging, and (4) hybridized 2DSemi, for photocatalytic CO2 conversion over the past few years. With a particular focus on highlighting the distinct advantages of SAs-2DSemi, we delve into the synthesis of state-of-the-art catalysts, their catalytic performances, and mechanistic elucidation facilitated by experimental characterizations and theoretical calculations. Following this, we outline the challenges in this field and offer perspectives on harnessing the potential of SAs-2DSemi as promising photocatalysts. This comprehensive review aims to provide valuable insights for the future development of 2D photocatalytic materials involving SAs for CO2 reduction.

High-Density Dual-Structure Single-Atom Pt Electrocatalyst for Efficient Hydrogen Evolution and Multimodal Sensing

Herein, we report a high-density dual-structure single-atom catalyst (SAC) by creating a large number of vacancies of O and Ti in two-dimensional (2D) Ti3C2 to immobilize Pt atoms (SA Pt-Ti3C2). The SA Pt-Ti3C2 showed excellent performance toward the pH-universal electrochemical hydrogen evolution reaction (HER) and multimodal sensing. For HER catalysis, compared to the commercial 20 wt % Pt/C, the Pt mass activities of SA Pt-Ti3C2 at the overpotentials of ∼30 and 110 mV in acid and alkaline media are 45 and 34 times higher, respectively. More importantly, during the alkaline HER process, an interesting synergetic effect between Pt-C and Pt-Ti sites that dominated the Volmer and Heyrovsky steps, respectively, was revealed. Moreover, the SA Pt-Ti3C2 catalyst exhibited high sensitivity (0.62-2.65 μA μM-1) and fast response properties for the multimodal identifications of ascorbic acid, dopamine, uric acid, and nitric oxide under the assistance of machine learning.

Interfacial Thermoconvection and Atomic Relay Catalysis Enable Equilibrium Shifting and Rapid Glucose-to-Fructose Isomerization

The aqueous glucose-to-fructose isomerization is controlled by thermodynamics to an equilibrium limit of ~50 % fructose yield. However, here we report an in situ fructose removal strategy enabled by an interfacial local photothermal effect in combination with relay catalysis of geminal and isolated potassium single atoms (K SAs) on graphene-type carbon (Ksg/GT) to effectively bypass the equilibrium limit and markedly speed up glucose-to-fructose isomerization. At 25 °C, an unprecedented fructose yield of 68.2 % was obtained over Ksg/GT in an aqueous solution without any additives under 30-min solar-like irradiation. Mechanistic studies expounded that the interfacial thermoconvection caused by the local photothermal effect of the graphene-type carbon and preferable glucose adsorption on single-atom K could facilitate the release of in situ formed fructose. The geminal K SAs were prone to form a stable metal-glucose complex via bidentate coordination, and could significantly reduce the C-H bond electron density by light-driven electron transfer toward K. This facilitated the hydride shift rate-determining step and expedited glucose isomerization. In addition, isolated K SAs favored the subsequent protonation and ring-closure process to furnish fructose. The integration of the interfacial thermoconvection-enhanced in situ removal protocol and tailored atomic catalysis opens a prospective avenue for boosting equilibrium-limited reactions under mild conditions.

Optimized Carbon Coupling for Enhanced Ethylene Production via a Unique Single-Atom-Substrate Synergy Mechanism within Photocatalytic Processes

The utilization of solar-driven technologies for the direct conversion of methanol (CH3OH) into two or multi-carbon compounds through controlled carbon-carbon (C-C) coupling is an appealing yet challenging objective. In this study, we successfully demonstrate the photocatalytic CH3OH coupling to ethylene (C2H4), a valuable chemical raw material, by employing a carbon nitride-based catalyst. Specifically, we modify the layered polymer carbon nitride (PCN) photocatalyst through the incorporation of Au single atoms (Au1/PCN) using a chemical-scissors method. The synergistic effect between the PCN substrate and the Au single atoms reduces the potential barrier associated with C-C coupling, thereby enhancing the efficiency of CH3OH reforming to C2H4. This investigation not only reveals a novel pathway for C2H4 production via CH3OH reforming but also provides fresh insights into the possibilities of C-C coupling.

Advances of Synergistic Electrocatalysis Between Single Atoms and Nanoparticles/Clusters

Combining single atoms with clusters or nanoparticles is an emerging tactic to design efficient electrocatalysts. Both synergy effect and high atomic utilization of active sites in the composite catalysts result in enhanced electrocatalytic performance, simultaneously provide a radical analysis of the interrelationship between structure and activity. In this review, the recent advances of single-atomic site catalysts coupled with clusters or nanoparticles are emphasized. Firstly, the synthetic strategies, characterization, dynamics and types of single atoms coupled with clusters/nanoparticles are introduced, and then the key factors controlling the structure of the composite catalysts are discussed. Next, several clean energy catalytic reactions performed over the synergistic composite catalysts are illustrated. Eventually, the encountering challenges and recommendations for the future advancement of synergistic structure in energy-transformation electrocatalysis are outlined.

Electrochemical Knocking-Down of Zn Metal Clusters into Single Atoms

Single Atoms Catalysts (SACs) have emerged as a class of highly promising heterogeneous catalysts, where the traditional bottom-up synthesis approaches often encounter considerable challenges in relation to aggregation issues and poor stability. Consequently, achieving densely dispersed atomic species in a reliable and efficient manner remains a key focus in the field. Herein, we report a new facile electrochemical knock-down strategy for the formation of SACs, whereby the metal Zn clusters are transformed into single atoms. While a defect-rich substrate plays a pivotal role in capturing and stabilizing isolated Zn atoms, the feasibility of this novel strategy is demonstrated through a comprehensive investigation, combining experimental and theoretical studies. Furthermore, when studied in exploring for potential applications, the material prepared shows a remarkable improvement of 58.21% for the Li+ storage and delivers a capacity over 300 Wh kg-1 after 500 cycles upon the transformation of Zn clusters into single atoms.

Exploring interfacial electrocatalysis for iodine redox conversion in zinc-iodine battery

The challenges posed by the non-conductive nature of iodine, coupled with the easy formation of soluble polyiodides in water, impede its integration with zinc for the development of advanced rechargeable batteries. Here we demonstrate the in-situ loading of molybdenum carbide nanoclusters (MoC) and zinc single atoms (Zn-SA) into porous carbon fibers to invoke electrocatalytic conversion of iodine at the interface. The electronic interactions between MoC and Zn-SA lead to an upshift in the d-band center of Mo relative to the Fermi level, thus promoting the interfacial interactions with iodine species to suppress shuttle effects. Notably, the optimal charge delocalization, induced by d-p orbital hybridization between molybdenum and iodine, also lowers the redox energy barrier to promote the interfacial conversion. With interfacial electrocatalysis minimizing polyiodide intermediates via a favorable redox conversion pathway, zinc-iodine batteries therefore demonstrate a large specific capacity of 230.6 mAh g-1 and the good capacity retention for 20,000 cycles.

Ball-milled prepared Fe3O4-FeSAs-NPs@NC catalyst synergistically facilitate the generation of reactive oxygen species for oxidative trifluoromethylation of alkenes

Heterogeneous catalysts have recently regarded as a promising chose for the thermally-driven generation of the reactive oxygen species (ROS) through catalytic reactions with molecular oxygen, which can facilitate this process by specific geometric and electronic structure. However, the oxidative trifluoromethylation of alkenes to α-trifluoromethylated ketones by CF3SO2Na is rarely reported in this system. In this work, we report a one-pot polymerization ball milling strategy to construct precursor, and then pyrolyze it to obtain specific carbon nanotubes matrix with Fe/Fe3O4 nanoparticles and single atoms Fe. Remarkably, the optimized catalyst (Fe3O4-FeSAs-NPs@NC-1) displays excellent catalytic performance, broad substrates and recyclability for this fluorination reaction via radical pathway. Based on characterizations and mechanistic studies, we discover that the coexistence of Fe/Fe3O4 and Fe-Nx not only synergistically facilitates the catalytic efficiency in altering the electronic structure of Fe sites, but also benefits the absorption of O2 and the ability of the thermally-driven generating ROS which can activate CF3SO2Na to CF3 radical. This work offers a method of designing Fe-based catalysts and also opens up a new thermal-heterogeneous catalysis way for the oxidative trifluoromethylation of alkenes.

Modulating the electronic configuration of single-atom nanozymes using cobalt nanoclusters for enhanced mycotoxin degradation

Herein, Co- and Fe-based single-atom nanozymes (M/N-PC, M = Co or Fe) were successfully fabricated and their catalytic performances for patulin degradation were evaluated systematically. Co/N-PC, consisting of Co-N4 and nanoclusters sites, achieved a higher patulin degradation efficiency (99.4 %, within 60 min) than Fe/N-PC (only consisting of Fe-N5 sites). Synergistic interactions between Co-N4 and Co nanoclusters greatly enhanced electron density near the Fermi level in Co/N-PC, enabling its high catalytic performance. The degradation products of patulin exhibited negligible cytotoxicity. The M/N-PCs demonstrated good reusability, broad pH adaptability and high practical application potential for patulin degradation in apple juice. M/N-PC also exhibited high efficiency in degrading aflatoxin B1, deoxynivalenol and zearalenone (∼100 %, 10-40 min). This study provides in-depth insights into the relationship between metal active site structures in M/N-PCs and their catalytic properties for mycotoxin detoxification, offering guidance for the design of highly efficient single-atom nanozymes.