Ultrafine Core@Shell Cu1Au1@Cu1Pd3 Nanodots Synergized with 3D Porous N-Doped Graphene Nanosheets as a High-Performance Multifunctional Electrocatalyst

Materials Containing Single-, Di-, Tri-, and Multi-Metal Atoms Bonded to C, N, S, P, B, and O Species as Advanced Catalysts for Energy, Sensor, and Biomedical Applications

Modifying the coordination or local environments of single-, di-, tri-, and multi-metal atom (SMA/DMA/TMA/MMA)-based materials is one of the best strategies for increasing the catalytic activities, selectivity, and long-term durability of these materials. Advanced sheet materials supported by metal atom-based materials have become a critical topic in the fields of renewable energy conversion systems, storage devices, sensors, and biomedicine owing to the maximum atom utilization efficiency, precisely located metal centers, specific electron configurations, unique reactivity, and precise chemical tunability. Several sheet materials offer excellent support for metal atom-based materials and are attractive for applications in energy, sensors, and medical research, such as in oxygen reduction, oxygen production, hydrogen generation, fuel production, selective chemical detection, and enzymatic reactions. The strong metal-metal and metal-carbon with metal-heteroatom (i.e., N, S, P, B, and O) bonds stabilize and optimize the electronic structures of the metal atoms due to strong interfacial interactions, yielding excellent catalytic activities. These materials provide excellent models for understanding the fundamental problems with multistep chemical reactions. This review summarizes the substrate structure-activity relationship of metal atom-based materials with different active sites based on experimental and theoretical data. Additionally, the new synthesis procedures, physicochemical characterizations, and energy and biomedical applications are discussed. Finally, the remaining challenges in developing efficient SMA/DMA/TMA/MMA-based materials are presented.

Regulation of the d-band center of metal-organic frameworks for energy-saving hydrogen generation coupled with selective glycerol oxidation

The hybrid electrolyzer coupled glycerol oxidation (GOR) with hydrogen evolution reaction (HER) is fascinating to simultaneously generate H2 and high value-added chemicals with low energy input, yet facing a challenge. Herein, Cu-based metal-organic frameworks (Cu-MOFs) are reported as model catalysts for both HER and GOR through doping of atomically dispersed precious and nonprecious metals. Remarkably, the HER activity of Ru-doped Cu-MOF outperformed a Pt/C catalyst, with its Faradaic efficiency for formate formation at 90% at a low potential of 1.40 V. Furthermore, the hybrid electrolyzer only needed 1.36 V to achieve 10 mA cm-2, 340 mV lower than that for splitting pure water. Theoretical calculations demonstrated that electronic interactions between the host and guest (doped) metals shifted downward the d-band centers (εd) of MOFs. This consequently lowered water adsorption and dissociation energy barriers and optimized hydrogen adsorption energy, leading to significantly enhanced HER activities. Meanwhile, the downshift of εd centers reduced energy barriers for rate-limiting step and the formation energy of OH*, synergistically enhancing the activity of MOFs for GOR. These findings offered an effective means for simultaneous productions of hydrogen fuel and high value-added chemicals using one hybrid electrolyzer with low energy input.

Self-Interface in Rh Nanosheets-Supported Tetrahedral Rh Nanocrystals for Promoting Electrocatalytic Oxidation of Ethanol

Direct ethanol fuel cells hold great promise as a power source. However, their commercialization is limited by anode catalysts with insufficient selectivity toward a complete oxidation of ethanol for a high energy density, as well as sluggish catalytic kinetics and low stability. To optimize the catalytic performance, rationally tuning surface structure or interface structure is highly desired. Herein, a facile route is reported to the synthesis of Rh nanosheets-supported tetrahedral Rh nanocrystals (Rh THs/NSs), which possess self-supporting homogeneous interface between Rh tetrahedrons and Rh nanosheets. Due to full leverage of the structural advantages within the given structure and construction of interfaces, the Rh THs/NSs can serve as highly active electro-catalysts with excellent mass activity and selectivity toward ethanol electro-oxidation. The in situ Fourier transform infrared reflection spectroscopy showed the Rh THs/NSs exhibit the highest C1 pathway selectivity of 23.2%, far exceeding that of Rh nanotetrahedra and Rh nanosheets. Density function theory calculations further demonstrated that self-interface between Rh nanosheets and tetrahedra is beneficial for C-C bond cleavage of ethanol. Meanwhile, the self-supporting of 2D nanosheets greatly enhance the stability of tetrahedra, which improves the catalytic stability.

A Facile Preparation of Sandwich-Structured Pd/Polypyrrole-Graphene/Pd Catalysts for Formic Acid Electro-Oxidation

Direct formic acid fuel cells (DFAFCs) are one of the most promising power sources due to its high conversion efficiency; relatively low carbon emissions, toxicity, and flammability; convenience; and low-cost storage and transportation. However, the key challenge to large-scale commercial applications is its poor power performance and the catalyst's high preparation cost. In this study, a new sandwich-structured Pd/polypyrrole-graphene/Pd (Pd/PPy-Gns/Pd)-modified glassy carbon electrode (GCE) was prepared using a simple constant potential (CP) electrodeposition technique. On the basis of the unique synthetic procedure and structural advantages, the Pd/PPy-Gns/Pd shows a fast charge/mass transport rate, high electrocatalytic activity, and great stability for formic acid electro-oxidation (FAO). The mass activity of Pd/PPy-Gns/Pd electrode reaches 917 mA·mg^-1_Pd. The excellent catalytic activity is mainly due to the uniform embedding of Pd nanoparticles on the polypyrrole-graphene (PPy-Gns) support, which exposes more active sites, and prevents the shedding and inactivation of Pd nanoparticles. At the same time, the introduction of graphene (Gns) in the PPy further improved the conductivity of the catalyst and accelerated the transfer of electrons.