Changlai Wang

Tuning the Activity of Carbon for Electrocatalytic Hydrogen Evolution via an Iridium‐Cobalt Alloy Core Encapsulated in Nitrogen‐Doped Carbon Cages

Graphene, a 2D material consisting of a single layer of sp2 -hybridized carbon, exhibits inert activity as an electrocatalyst, while the incorporation of heteroatoms (such as N) into the framework can tune its electronic properties. Because of the different electronegativity between N and C atoms, electrons will transfer from C to N in N-doped graphene nanosheets, changing inert C atoms adjacent to the N-dopants into active sites. Notwithstanding the achieved progress, its intrinsic activity in acidic media is still far from Pt/C. Here, a facile annealing strategy is adopted for Ir-doped metal-organic frameworks to synthesize IrCo nanoalloys encapsulated in N-doped graphene layers. The highly active electrocatalyst, with remarkably reduced Ir loading (1.56 wt%), achieves an ultralow Tafel slope of 23 mV dec-1 and an overpotential of only 24 mV at a current density of 10 mA cm-2 in 0.5 m sulfuric acid solution. Such superior performance is even superior to the noble-metal catalyst Pt. Surface structural and computational studies reveal that the superior behavior originates from the decreased ΔGH* for HER induced by the electrons transferred from the alloy core to the graphene layers, which is beneficial for enhancing CH binding.

Enhanced CO oxidation on CeO2/Co3O4 nanojunctions derived from annealing of metal organic frameworks

The interface of nanojunctions plays an important role in the performance of heterogeneous catalysts. However, it is highly challenging to construct nanojunctions which are usually prepared by complex multistep processes. Metal-organic frameworks (MOFs), with designable metal centers and tunable organic ligands, are promising precursors for the one-step synthesis of nanojunctions. Herein, we prepared porous CeO2/Co3O4 nanojunctions by direct annealing of MOFs in air. These unique nanojunctions exhibit remarkable catalytic activity for CO oxidation, which can achieve complete oxidization of CO to CO2 at 110 °C. In contrast, the temperature required for 100% CO oxidation is 190 °C for pure Co3O4. Moreover, the nanojunctions can maintain complete CO conversion after 16 h at 110 °C. Density functional theory calculations revealed that the enhancement in the catalytic activity of CeO2/Co3O4 nanojunctions can be attributed to the charge transfer through the interfaces of the nanojunctions.

Interface engineering of Ru–Co3O4 nanocomposites for enhancing CO oxidation

The interfacial structure plays an important role in heterogeneous catalysis due to its unique electronic structure. However, the design of interfacial structures with high activity remains a challenge because the fundamental nature of the active catalytic sites and the details of the reaction mechanism are still hotly debated. Herein, we combine experiment and density functional theory calculations to reveal the catalytic mechanism for the oxidation of CO by constructing a Ru–Co3O4 interface. Experimental results show that CO oxidation can be significantly enhanced at the interface. Density functional theory calculations indicate that this enhancement is attributed to the charge transfer from ruthenium to Co3O4. As a result, O2 is facilely activated by ruthenium with adjacent Co at the interface, hence lowering the activation energy and boosting the catalytic performance of CO oxidation. This study provides a new way to design and develop efficient catalysts by engineering an appropriate interface.

O-, N-Atoms-Coordinated Mn Cofactors within a Graphene Framework as Bioinspired Oxygen Reduction Reaction Electrocatalysts

Manganese (Mn) is generally regarded as not being sufficiently active for the oxygen reduction reaction (ORR) compared to other transition metals such as Fe and Co. However, in biology, manganese-containing enzymes can catalyze oxygen-evolving reactions efficiently with a relative low onset potential. Here, atomically dispersed O and N atoms coordinated Mn active sites are incorporated within graphene frameworks to emulate both the structure and function of Mn cofactors in heme-copper oxidases superfamily. Unlike previous single-metal catalysts with general M-N-C structures, here, it is proved that a coordinated O atom can also play a significant role in tuning the intrinsic catalytic activities of transition metals. The biomimetic electrocatalyst exhibits superior performance for the ORR and zinc-air batteries under alkaline conditions, which is even better than that of commercial Pt/C. The excellent performance can be ascribed to the abundant atomically dispersed Mn cofactors in the graphene frameworks, confirmed by various characterization methods. Theoretical calculations reveal that the intrinsic catalytic activity of metal Mn can be significantly improved via changing local geometry of nearest coordinated O and N atoms. Especially, graphene frameworks containing the Mn-N3 O1 cofactor demonstrate the fastest ORR kinetics due to the tuning of the d electronic states to a reasonable state.

Ultrasmall Ru/Cu-doped RuO2 Complex Embedded in Amorphous Carbon Skeleton as Highly Active Bifunctional Electrocatalysts for Overall Water Splitting

Developing highly active electrocatalysts with superior durability for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in the same electrolyte is a grand challenge to realize the practical application of electrolysis water for producing hydrogen. In this work, an ultrasmall Ru/Cu-doped RuO2 complex embedded in an amorphous carbon skeleton is synthesized, through thermolysis of Ru-modified Cu-1,3,5-benzenetricarboxylic acid (BTC), as a highly efficient bifunctional catalyst for overall water splitting electrocatalysis. The ultrasmall Ru nanoparticles in the complex expose more activity sites for hydrogen evolution and outperform the commercial Pt/C. Meanwhile, the ultrasmall RuO2 nanoparticles exhibit superior oxygen evolution performance over commercial RuO2, and the doping of Cu into the ultrasmall RuO2 nanoparticles further enhances the oxygen evolution performance of the catalyst. The outstanding OER and decent HER catalytic activity endow the complex with impressive overall water splitting performance superior to that of the state-of-the-art electrocatalysts, which just require 1.47 and 1.67 V to achieve a current density of 10 mA cm-2 and 100 mA cm-2. The density functional theory calculations reveal that a Cu dopant could effectively tailor the d-band center, thereby tuning electronic structure of Ru activity sites on the RuO2 (110) plane and ultimately improving the OER performance of RuO2.

Incorporation of Cu-Nx cofactors into graphene encapsulated Co as biomimetic electrocatalysts for efficient oxygen reduction

Unlike metals with incomplete d-shells such as Pt and Fe, copper (Cu) with a filled d-electron shell is generally regarded as a sluggish oxygen reduction reaction (ORR) electrocatalyst. However, laccase and other copper enzymes could catalyze the ORR efficiently in nature. Inspired by this, we incorporated Cu-Nx cofactors (Cu-N2 and Cu-N4) into graphene encapsulated Co frameworks by direct annealing of MOFs with a post etching process. The bioinspired electrocatalyst exhibits excellent performance and stability for ORR which is comparable to or even better than Pt/C. Meanwhile, it also illustrates a fantabulous performance in a zinc-air battery device. The excellent performance can be ascribed to the abundant atomically dispersed Cu-Nx cofactors in the graphene frameworks confirmed by aberration corrected HAADF-STEM and XAFS analyses. Density functional theory calculations suggest that when Cu atoms are coordinated with the surrounding N atoms, the valence electrons of Cu atoms will transfer to nitrogen atoms, simultaneously tuning the d electronic states near the Fermi level to realize fast ORR kinetics.

Metallic 1T phase MoS2 nanosheets decorated hollow cobalt sulfide polyhedra for high-performance lithium storage

Transition metal sulfides have attracted tremendous attention as promising lithium-ion anodes due to their natural abundance, intrinsic safety and high theoretical capacity. However, low conductivity and dramatic volume variation hinder their further application in lithium storage. Here, we reported a facile metal–organic framework (MOF)-derived self-template approach to prepare hollow cobalt sulfide polyhedra with vertically aligned metallic phase MoS2 nanosheets (denoted as CoS@1T-MoS2) as efficient anode materials for lithium storage. Benefiting from the high intrinsic conductivity of metallic phase MoS2, the hierarchical hollow framework, and the synergistic effect of interior cobalt sulfide and exterior metallic MoS2, the CoS@1T-MoS2 composite delivers a high reversible capacity of 1269 mA h g−1 after 100 cycles at a current density of 100 mA g−1 and 936 mA h g−1 at a current density of 1000 mA g−1 after 220 cycles.

Designing highly efficient dual-metal single-atom electrocatalysts for the oxygen reduction reaction inspired by biological enzyme systems

Biological heme–copper oxidases (HCOs) play a critical role in the four-electron, four-proton reduction of O2 to H2O in biosystems. HCOs exhibit high enzymatic activity due to their natural structure with heme–non-heme metal active sites, and the non-heme metal plays a role in conferring and fine-tuning the O2 reduction activity of the HCOs. Inspired by this binuclear active enzyme, herein, we designed an efficient electrocatalyst (Fe, Mn–N/C) for the oxygen reduction reaction, which contains two types of metal–Nx active site incorporated within the graphene framework of porous carbon. The catalyst displayed remarkable ORR performance with a half-potential of 0.904 V and kinetic current density of 33.33 mA cm−2, which is 4.9 times that of 20% Pt/C (6.76 mA cm−2). When the Fe, Mn–N/C catalyst was applied as an air electrode in a Zn–air battery, it exhibited a superior performance compared to commercial Pt/C. Its discharge curve showed that the change in output voltage was negligible at 20 mA cm−2 for 23 000 seconds (6.4 h). First principles calculations revealed that Fe, Mn–N/C needs less energy for the protonation of O* to OH* in ORR procedures compared with Fe–N/C. This catalyst, with its bimetal reactive center mimicking a metal enzyme, will pave a new way to design efficient electrocatalysts for the ORR in fuel cells.

In Situ One-Pot Synthesis of MOF-Polydopamine Hybrid Nanogels with Enhanced Photothermal Effect for Targeted Cancer Therapy

Abstract Herein, a simple one‐pot way is designed to prepare a type of multifunctional metal–organic framework (MOF)‐based hybrid nanogels by in situ hybridization of dopamine monomer in the skeleton of MnCo. The resultant hybrid nanoparticles (named as MCP) show enhanced photothermal conversion efficiency in comparison with pure polydopamine or MnCo nanoparticles (NPs) synthesized under a similar method and, therefore, show great potential for photothermal therapy (PTT) in vivo. The MCP NPs are expected to possess T 1 positive magnetic resonance imaging ability due to the high‐spin Mn‐N6 (S = 5/2) in the skeleton of MnCo. To improve the therapy efficiency as a PTT agent, the MCP NPs are further modified with functional polyethylene glycol (PEG) and thiol terminal cyclic arginine–glycine–aspartic acid peptide, respectively: the first one is to increase the stability, biocompatibility, and blood circulation time of MCP NPs in vivo; the second one is to increase the tumor accumulation of MCP‐PEG NPs and improve their therapeutic efficiency as photothermal agent.