Engineering the Local Atomic Environments of Indium Single‐Atom Catalysts for Efficient Electrochemical Production of Hydrogen Peroxide

Efficient catalytic oxidation of formaldehyde by defective g-C3N4-anchored single-atom Pt: A DFT study

Indoor volatile formaldehyde is a serious health hazard. The development of low-temperature and efficient nonhomogeneous oxidation catalysts is crucial for protecting human health and the environment but is also quite challenging. Single-atom catalysts (SACs) with active centers and coordination environments that are precisely tunable at the atomic level exhibit excellent catalytic activity in many catalytic fields. Among two-dimensional materials, the nonmagnetic monolayer material g-C3N4 may be a good platform for loading single atoms. In this study, the effect of nitrogen defect formation on the charge distribution of g-C3N4 is discussed in detail using density functional theory (DFT) calculations. The effect of nitrogen defects on the activated molecular oxygen of Pt/C3N4 was systematically revealed by DFT calculations in combination with molecular orbital theory. Two typical reaction mechanisms for the catalytic oxidation of formaldehyde were proposed based on the Eley-Rideal (E-R) mechanism. Pt/C3N4-V3N was more advantageous for path 1, as determined by the activation energy barrier of the rate-determining step and product desorption. Finally, the active centers and chemical structures of Pt/C3N4 and Pt/C3N4-V3N were verified to have good stability at 375 K by determination of the migration energy barriers and ab initio molecular dynamics simulations. Therefore, the formation of N defects can effectively anchor single-atom Pt and provide additional active sites, which in turn activate molecular oxygen to efficiently catalyze the oxidation of formaldehyde. This study provides a better understanding of the mechanism of formaldehyde oxidation by single-atom Pt catalysts and a new idea for the development of Pt as well as other metal-based single-atom oxidation catalysts.

Efficient Neutral H2O2 Electrosynthesis from Favorable Reaction Microenvironments via Porous Carbon Carrier Engineering

The efficient electrosynthesis of hydrogen peroxide (H2O2) via two-electron oxygen reduction reaction (2e- ORR) in neutral media is undoubtedly a practical route, but the limited comprehension of electrocatalysts has hindered the system advancement. Herein, we present the design of model catalysts comprising mesoporous carbon spheres-supported Pd nanoparticles for H2O2 electrosynthesis at near-zero overpotential with approximately 95 % selectivity in a neutral electrolyte. Impressively, the optimized Pd/MCS-8 electrocatalyst in a flow cell device achieves an exceptional H2O2 yield of 15.77 mol gcatalyst -1 h-1, generating a neutral H2O2 solution with an accumulated concentration of 6.43 wt %, a level sufficiently high for medical disinfection. Finite element simulation and experimental results suggest that mesoporous carbon carriers promote O2 enrichment and localized pH elevation, establishing a favorable microenvironment for 2e- ORR in neutral media. Density functional theory calculations reveal that the robust interaction between Pd nanoparticles and the carbon carriers optimized the adsorption of OOH* at the carbon edge, ensuring high active 2e- process. These findings offer new insights into carbon-loaded electrocatalysts for efficient 2e- ORR in neutral media, emphasizing the role of carrier engineering in constructing favorable microenvironments and synergizing active sites.

Microwave-Assisted Rapid Synthesis of MOF-Based Single-Atom Ni Catalyst for CO2 Electroreduction at Ampere-Level Current

Carbon-based single-atom catalysts (SACs) have attracted tremendous interest in heterogeneous catalysis. However, the common electric heating techniques to produce carbon-based SACs usually suffer from prolonged heating time and tedious operations. Herein, a general and facile microwave-assisted rapid pyrolysis method is developed to afford carbon-based SACs within 3 min without inert gas protection. The obtained carbon-based SACs present high porosity and comparable carbonization degree to those obtained by electric heating techniques. Specifically, the single-atom Ni implanted N-doped carbon (Ni1 -N-C) derived from a Ni-doped metal-organic framework (Ni-ZIF-8) exhibits remarkable CO Faradaic efficiency (96 %) with a substantial CO partial current density (jCO ) up to 1.06 A/cm2 in CO2 electroreduction, far superior to the counterpart obtained by traditional pyrolysis with electric heating. Mechanism investigations reveal that the resulting Ni1 -N-C presents abundant defective sites and mesoporous structure, greatly facilitating CO2 adsorption and mass transfer. This work establishes a versatile approach to rapid and large-scale synthesis of SACs as well as other carbon-based materials for efficient catalysis.

Nanoengineering of Porous 2D Structures with Tunable Fluid Transport Behavior for Exceptional H2O2 Electrosynthesis

Precision nanoengineering of porous two-dimensional structures has emerged as a promising avenue for finely tuning catalytic reactions. However, understanding the pore-structure-dependent catalytic performance remains challenging, given the lack of comprehensive guidelines, appropriate material models, and precise synthesis strategies. Here, we propose the optimization of two-dimensional carbon materials through the utilization of mesopores with 5-10 nm diameter to facilitate fluid acceleration, guided by finite element simulations. As proof of concept, the optimized mesoporous carbon nanosheet sample exhibited exceptional electrocatalytic performance, demonstrating high selectivity (>95%) and a notable diffusion-limiting disk current density of -3.1 mA cm-2 for H2O2 production. Impressively, the electrolysis process in the flow cell achieved a production rate of 14.39 mol gcatalyst-1 h-1 to yield a medical-grade disinfectant-worthy H2O2 solution. Our pore engineering research focuses on modulating oxygen reduction reaction activity and selectivity by affecting local fluid transport behavior, providing insights into the mesoscale catalytic mechanism.

Single-Atom Gadolinium Nano-Contrast Agents with High Stability for Tumor T1 Magnetic Resonance Imaging

Gadolinium chelates for tumor magnetic resonance imaging (MRI) face challenges such as inadequate sensitivity, lack of selectivity, and risk of Gd leakage. This study presents a single-atom Gd nano-contrast agent (Gd-SA) that enhances tumor MRI. Isolated Gd atoms coordinated by six N atoms and two O atoms are atomically dispersed on a hollow carbon nanosphere, allowing the maximum utilization of Gd atoms with reduced risk of toxic Gd ion leakage. Owning to the large surface area and fast exchange of relaxed water molecules, Gd-SA shows excellent T₁-weighted magnetic resonance enhancement with a r₁ value of 11.05 mM^-1 s^-1 at 7 T, which is 3.6 times that of the commercial gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA). In vivo MRI results show that the Gd-SA has a higher spatial resolution and a wider imaging time window for tumors than Gd-DTPA, with low hematological, hepatic, and nephric toxicities. These advantages demonstrate the great potential of single-atom Gd-based nanomaterials as safe, efficient, and long-term MRI contrast agents for cancer diagnosis.

Single-Atom Yttrium Engineering Janus Electrode for Rechargeable Na-S Batteries

The development of rechargeable Na-S batteries is very promising, thanks to their considerably high energy density, abundance of elements, and low costs and yet faces the issues of sluggish redox kinetics of S species and the polysulfide shuttle effect as well as Na dendrite growth. Following the theory-guided prediction, the rare-earth metal yttrium (Y)-N₄ unit has been screened as a favorable Janus site for the chemical affinity of polysulfides and their electrocatalytic conversion, as well as reversible uniform Na deposition. To this end, we adopt a metal-organic framework (MOF) to prepare a single-atom hybrid with Y single atoms being incorporated into the nitrogen-doped rhombododecahedron carbon host (Y SAs/NC), which features favorable Janus properties of sodiophilicity and sulfiphilicity and thus presents highly desired electrochemical performance when used as a host of the sodium anode and the sulfur cathode of a Na-S full cell. Impressively, the Na-S full cell is capable of delivering a high capacity of 822 mAh g^-1 and shows superdurable cyclability (97.5% capacity retention over 1000 cycles at a high current density of 5 A g^-1). The proof-of-concept three-dimensional (3D) printed batteries and the Na-S pouch cell validate the potential practical applications of such Na-S batteries, shedding light on the development of promising Na-S full cells for future application in energy storage or power batteries.

Main-Group Catalysts with Atomically Dispersed In Sites for Highly Efficient Oxidative Dehydrogenation

Transition metal oxides are well-known catalysts for oxidative dehydrogenation thanks to their excellent ability to activate alkanes. However, they suffer from an inferior alkene yield due to the trade-off between the conversion and selectivity induced by more reactive alkenes than alkanes, which obscures the optimization of catalysts. Herein, we attempt to overcome this challenge by activating a selective main-group indium oxide considered to be inactive for oxidative dehydrogenation in conventional wisdom. Atomically dispersed In sites with the local structure of [InOH]²⁺ anchored by substituting the protons of supercages in HY are enclosed to be active centers that enable the activation of ethane with a metal-normalized turnover number of almost one magnitude higher than those of their supported In₂O₃ counterparts. Furthermore, the structure of isolated [InOH]²⁺ sites could be stabilized by in situ formed H₂O from the selective oxidation of hydrogen by In₂O₃ nanoparticles. As a result, the as-designed main-group In catalysts exhibit 80% ethene selectivity at 80% ethane conversion, thus achieving 60% ethene yield due to active isolated [InOH]²⁺ sites and selective In₂O₃ nanoparticles, outperforming state-of-the-art transition metal oxide catalysts. This study unlocks new opportunities for the utilization of main-group elements and could pave the way toward a more rational design of catalysts for highly efficient selective oxidation catalysis.