A general strategy for preparing pyrrolic-N4 type single-atom catalysts via pre-located isolated atoms.

Single-atom catalysts (SACs) have been applied in many fields due to their superior catalytic performance. Because of the unique properties of the single-atom-site, using the single atoms as catalysts to synthesize SACs is promising. In this work, we have successfully achieved Co1 SAC using Pt1 atoms as catalysts. More importantly, this synthesis strategy can be extended to achieve Fe and Ni SACs as well. X-ray absorption spectroscopy (XAS) results demonstrate that the achieved Fe, Co, and Ni SACs are in a M1-pyrrolic N4 (M= Fe, Co, and Ni) structure. Density functional theory (DFT) studies show that the Co(Cp)2 dissociation is enhanced by Pt1 atoms, thus leading to the formation of Co1 atoms instead of nanoparticles. These SACs are also evaluated under hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), and the nature of active sites under HER are unveiled by the operando XAS studies. These new findings extend the application fields of SACs to catalytic fabrication methodology, which is promising for the rational design of advanced SACs.

Unveiling the Nature of Pt Single-Atom Catalyst during Electrocatalytic Hydrogen Evolution and Oxygen Reduction Reactions.

Single-atom catalysts (SACs) have attracted significant attention due to their superior catalytic activity and selectivity. However, the nature of active sites of SACs under realistic reaction conditions is ambiguous. In this work, high loading Pt single atoms on graphitic carbon nitride (g-C3 N4 )-derived N-doped carbon nanosheets (Pt1 /NCNS) is achieved through atomic layer deposition. Operando X-ray absorption spectroscopy (XAS) is performed on Pt single atoms and nanoparticles (NPs) in both the hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR). The operando results indicate that the total unoccupied density of states of Pt 5d orbitals of Pt1 atoms is higher than that of Pt NPs under HER condition, and that a stable Pt oxide is formed during ORR on Pt1 /NCNS, which may suppress the adsorption and activation of O2 . This work unveils the nature of Pt single atoms under realistic HER and ORR conditions, providing a deeper understanding for designing advanced SACs.

New Insight of Pyrrole-Like Nitrogen for Boosting Hydrogen Evolution Activity and Stability of Pt Single Atoms.

Single atomic Pt catalysts exhibit particularly high hydrogen evolution reaction (HER) activity compared to conventional nanomaterial-based catalysts. However, the enhanced mechanisms between Pt and their coordination environment are not understood in detail. Hence, a systematic study examining the different types of N in the support is essential to clearly demonstrate the relationship between Pt single atoms and N-doped support. Herein, three types of carbon nanotubes with varying types of N (pyridine-like N, pyrrole-like N, and quaternary N) are used as carbon support for Pt single atom atomic layer deposition. The detailed coordination environment of the Pt single atom catalyst is carefully studied by electron microscope and X-ray absorption spectra (XAS). Interestingly, with the increase of pyrrole-like N in the CNT support, the HER activity of the Pt catalyst also improves. First principle calculations results indicate that the interaction between the dyz and s orbitals of H and sp3 hybrid orbital of N should be the origin of the superior HER performance of these Pt single atom catalysts (SACs).

Engineering the Low Coordinated Pt Single Atom to Achieve the Superior Electrocatalytic Performance toward Oxygen Reduction.

Configuring metal single-atom catalysts (SACs) with high electrocatalytic activity and stability is one efficient strategy in achieving the cost-competitive catalyst for fuel cells' applications. Herein, the atomic layer deposition (ALD) strategy for synthesis of Pt SACs on the metal-organic framework (MOF)-derived N-doped carbon (NC) is proposed. Through adjusting the ALD exposure time of the Pt precursor, the size-controlled Pt catalysts, from Pt single atoms to subclusters and nanoparticles, are prepared on MOF-NC support. X-ray absorption fine structure spectra determine the increased electron vacancy in Pt SACs and indicate the Pt-N coordination in the as-prepared Pt SACs. Benefiting from the low-coordination environment and anchoring interaction between Pt atoms and nitrogen-doping sites from MOF-NC support, the Pt SACs deliver an enhanced activity and stability with 6.5 times higher mass activity than that of Pt nanoparticle catalysts in boosting the oxygen reduction reaction (ORR). Density functional theory calculations indicate that Pt single atoms prefer to be anchored by the pyridinic N-doped carbon sites. Importantly, it is revealed that the electronic structure of Pt SAs can be adjusted by adsorption of hydroxyl and oxygen, which greatly lowers free energy change for the rate-determining step and enhances the activity of Pt SACs toward the ORR.

Suppressing Corrosion of Aluminum Foils via Highly Conductive Graphene-like Carbon Coating in High-Performance Lithium-Based Batteries.

Aluminum foil is the predominant cathodic current collector in lithium-based batteries due to the high electronic conductivity, stable chemical/electrochemical properties, low density, and low cost. However, with the development of next-generation lithium batteries, Al current collectors face new challenges, such as the requirement of increased chemical stability at high voltage, long-cycle-life batteries with different electrolyte systems, as well as improved electronic conductivity and adhesion for new electrode materials. In this study, we demonstrate a novel graphene-like carbon (GLC) coating on the Al foil in lithium-based batteries. Various physical and electrochemical characterizations are conducted to reveal the electronic conductivity and electrochemical stability of the GLC-Al foil in both carbonate- and ether-based electrolytes. Full-cell tests, including Li-S batteries and high-voltage Li-ion batteries, are performed to demonstrate the significantly improved cycling and rate performance of batteries with the use of the GLC-Al foil as current collectors. The cell using the GLC-Al foil can greatly reduce the potential polarization in Li-S batteries and can obtain a reversible capacity of 750 mAh g-1 over 100 cycles at 0.5C. Even with high-sulfur-loading cathodes, the Li-S battery at 1C still maintains over 500 mAh g-1 after 100 cycles. In high-voltage Li-ion batteries, the GLC-Al foil significantly improves the high-rate performance, showing an increased retained capacity by over 100 mAh g-1 after 450 cycles at 1C compared to the bare foil. It is believed that the developed GLC-Al foil brings new opportunities to enhance the battery life of lithium-based batteries.