Single atom catalysts exhibit particularly high catalytic activities in contrast to regular nanomaterial-based catalysts. Until recently, research has been mostly focused on single atom catalysts, and it remains a great challenge to synthesize bimetallic dimer structures. Herein, we successfully prepare high-quality one-to-one A-B bimetallic dimer structures (Pt-Ru dimers) through an atomic layer deposition (ALD) process. The Pt-Ru dimers show much higher hydrogen evolution activity (more than 50 times) and excellent stability compared to commercial Pt/C catalysts. X-ray absorption spectroscopy indicates that the Pt-Ru dimers structure model contains one Pt-Ru bonding configuration. First principle calculations reveal that the Pt-Ru dimer generates a synergy effect by modulating the electronic structure, which results in the enhanced hydrogen evolution activity. This work paves the way for the rational design of bimetallic dimers with good activity and stability, which have a great potential to be applied in various catalytic reactions.

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nanoparticles (NPs) catalysts, SACs display unique features like their unsaturatedcoordination configuration, quantum size effect, and strong atom-support interaction, which induce the single-atom sites with excellent activity and stability in electrocatalysis. [1b,2] In 2011, Zhang and co-workers employed a coprecipitation method to prepare Pt SACs supported on iron oxide which demonstrated high activity and stability for CO oxidation. [3] Sun and co-workers reported the fabrication of Pt SACs on graphene by atomic layer deposition, and the as-prepared Pt SACs showed 10 times higher activity for methanol oxidation and superior CO tolerance compared to the benchmark Pt/C catalyst. [4] According to this research, it can be seen that "single atom catalysts" developed rapidly and have become a hot research topic in heterogeneous electrocatalysis. 1.1. Identification and Features of SACs SACs have isolated metal atoms that are anchored on a specific support and can behave as active centers for heterogeneous catalysis. The concept of single-atom catalysts can be traced back to the pioneering research reported by Zhang and co-workers in 2011. In their work, well-dispersed Pt single atoms were successfully prepared on the FeOx support, which opens the avenue of "single atom catalysts." The active single-atom sites generally consist of metal atoms and neighboring atoms from support materials. In addition, ion-exchanged metal atoms located on a porous support, as well as organometallic complexes anchored to the substrate, in principle, could also be viewed as SACs. The unique features of single atoms are significantly different from NPs, which endow SACs with exceptional catalytic activity, stability and selectivity. i) Decreasing the size of metal particles down to single atoms results in the maximum atom-utilization efficiency and metal dispersion. Owing to the low-coordination environment property and fully exposed active sites, SACs are capable to exhibit remarkable electrocatalytic activity toward diverse reactions. [5] ii) Single metal atoms can coordinate with support materials via strong interaction or charge transfer, which ensure the atomic dispersion and enhanced stability of SACs. [6] iii) The uniform active sites and geometric configuration of SACs enable similar electronic and spatial interactions with reactant molecules, thereby achieving Electrocatalysis plays a critical role in clean energy conversion, enabling great improvement for future sustainable technologies. Single atom catalysts (SACs) derived from metal-organic framework (MOF) are emerging extraordinary materials in electrochemical catalytic applications. Covering the merits of unique electronic structure, low-coordination environment, quantum size effect, and metal-support interaction, SACs promise enhanced electrocatalytic activity, stability, and selectivity in the field of clean energy conversion. In this article, MOF synthesis routes to afford well-dispersed SACs along with the respective synthesis mechanism are systematically reviewed first...

Lithium–sulfur batteries are deemed as optimal energy devices for the next generation of high‐energy‐density energy storage. However, several problems such as low energy density and short cycle life hinder their application in industry. Here, MoS2–MoN heterostructure nanosheets grown on carbon nanotube arrays as free‐standing cathodes are reported. In this heterostructure, MoN works as a promoter to provide coupled electrons to accelerate the redox reaction of polysulfides while the MoS2, with a two‐dimensional layered structure, provides smooth Li+ diffusion pathways. Through their respective advantages, both MoN and MoS2 could mutually boost the process of “adsorption‐diffusion‐conversion” of polysulfides, which have a synergy enhancement effect to restrain the lithium polysulfides from shuttling. The designed cathodes show excellent long‐term cycling performances of 1000 cycles at 1C with a low decay rate of 0.039% per cycle and a high rate capability up to 6C. A high initial areal capacity of 13.3 mAh cm−2 is also achieved under a low electrolyte volume/sulfur loading (E/S) ratio of 6.3 mL g−1. This strategy of promoting polysulfide conversion by heterostructure MoS2–MoN as presented in this work can provide a more structured design strategy for future advanced Li–S energy storage systems.

Pt single-atom catalysts are receiving more and more attention due to their different properties compared with nanostructures. As one typical kind of single-atom catalysts, Pt-based single-atom alloys (SAAs) have generated significant interest due to their application in several heterogeneous catalytic reactions. However, almost all of the reported Pt-based SAAs are on Cu surface. In addition, it is still great challenge to apply Pt single-atom alloys in electrocatalytic reactions. Herein, we demonstrated a fabrication of Pt/Pd SAA catalysts on nitrogen-doped carbon nanotubes by atomic layer deposition. The asprepared octahedral Pt/Pd SAA catalysts exhibited greatly improved activity compared to commercial Pt/C catalysts for electrochemical catalytic reactions. According to the X-ray adsorption spectrum, the Pt atoms in Pt/Pd SAA catalysts exhibited higher unoccupied 5d character density of states and a lower Pt−Pt coordination number, compared to those in core−shell structures. In addition, we used density functional theory calculation results to explain the enhanced mechanism of Pt/Pd SAA catalysts for electrochemical reactions. This study opens up an avenue of developing different types of Pt-based catalysts for electrocatalytic reactions and brings insight understanding about catalytic performances of SAA catalysts.

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.

Developing a low cost, highly active and durable cathode material is a high-priority research direction toward the commercialization of low-temperature fuel cells. However, the high cost and low stability of useable materials remain a considerable challenge for the widespread adoption of fuel cell energy conversion devices. The electrochemical performance of fuel cells is still largely hindered by the high loading of noble metal catalyst (Pt/Pt alloy) at the cathode, which is necessary to facilitate the inherently sluggish oxygen reduction reaction (ORR). Under these circumstances, the exploration of alternatives to replace expensive Pt-alloy for constructing highly efficient non-noble metal catalysts has been studied intensively and received great interest. Metal-organic frameworks (MOFs) a novel type of porous crystalline materials, have revealed potential application in the field of clean energy and demonstrated a number of advantages owing to their accessible high surface area, permanent porosity, and abundant metal/organic species. Recently, newly emerging MOFs materials have been used as templates and/or precursors to fabricate porous carbon and related functional nanomaterials, which exhibit excellent catalytic activities toward ORR or oxygen evolution reaction (OER). In this review, recent advances in the use of MOF-derived functional nanomaterials as efficient electrocatalysts in fuel cells are summarized. Particularly, we focus on the rational design and synthesis of highly active and stable porous carbon-based electrocatalysts with various nanostructures by using the advantages of MOFs precursors. Finally, further understanding and development, future trends, and prospects of advanced MOF-derived nanomaterials for more promising applications of clean energy are presented.

The development of highly efficient electrocatalysts toward the oxygen evolution reaction is imperative for advancing water splitting technology to generate clean hydrogen energy. Herein, a two dimensional (2D) nanosheet ammonium cobalt phosphate hydrate (NH 4 CoPO 4 •H 2 O) catalyst based on the earth-abundant non-noble metal is reported. When used for the challenging alkaline saline water electrolysis, the NH 4 CoPO 4 •H 2 O catalyst with the optimal thickness of 30 nm achieves current densities of 10 and 100 mA cm −2 at the record low overpotentials of 252 and 268 mV, respectively, while maintaining remarkable stability during the alkaline saline water oxidation at room temperature. X-ray absorption fine spectra reveal that the activation of Co (II) ions (in NH 4 CoPO 4 •H 2 O) to Co (III) species constructs the electrocatalytic active sites. The 2D nanosheet morphology of NH 4 CoPO 4 •H 2 O provides a larger active surface area and more surface-exposed active sites, which enable the nanosheet catalyst to facilitate the alkaline freshwater and simulated seawater oxidation with excellent activity. The facile and environmentally-benign H 2 O-mediated synthesis route under mild condition makes NH 4 CoPO 4 •H 2 O catalyst highly feasible for practical manufacturing. In comparison with noble metals, this novel electrocatalyst offers a cost-effective alternative for economic saline water oxidation to advance water electrolysis technology.