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1. Bimetallic Zeolitic Imidazolite Framework Derived Carbon Nanotubes Embedded with Co Nanoparticles for Efficient Bifunctional Oxygen Electrocatalyst

   https://doi.org/10.1002/aenm.201702048  

   Li, Yinle ; Jia, Baoming ; Fan, Yanzhong ; Zhu, Kelong ; Li, Guangqin ; Su, Cheng‐Yong ( December 2017 , Advanced Energy Materials)

   Bifunctional oxygen catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) with high activities and low‐cost are of prime importance and challenging in the development of fuel cells and rechargeable metal–air batteries. This study reports a porous carbon nanomaterial loaded with cobalt nanoparticles (Co@NC‐x/y) derived from pyrolysis of a Co/Zn bimetallic zeolitic imidazolite framework, which exhibits incredibly high activity as bifunctional oxygen catalysts. For instance, the optimal catalyst of Co@NC‐3/1 has the interconnected framework structure between porous carbon and embedded carbon nanotubes, which shows the superb ORR activity with onset potential of ≈1.15 V and half‐wave potential of ≈0.93 V. Moreover, it presents high OER activity that can be further enhanced to over commercial RuO₂by P‐doped with overpotentials of 1.57 V versus reversible hydrogen electrode at 10 mA cm⁻²and long‐term stability for 2000 circles and a Tafel slope of 85 mV dec⁻¹. Significantly, the nanomaterial demonstrates better catalytic performance and durability than Pt/C for ORR and commercial RuO₂and IrO₂for OER. These findings suggest the importance of a synergistic effect of graphitic carbon, nanotubes, exposed Co–N_xactive sites, and interconnected framework structure of various carbons for bifunctional oxygen electrocatalysts.

    

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2. Atomic and Molecular Layer Deposition of Hybrid Mo–Thiolate Thin Films with Enhanced Catalytic Activity

   https://doi.org/10.1002/adfm.201800852  

   MacIsaac, Callisto ; Schneider, Joel R. ; Closser, Richard G. ; Hellstern, Thomas R. ; Bergsman, David S. ; Park, Joonsuk ; Liu, Yunzhi ; Sinclair, Robert ; Bent, Stacey F. ( April 2018 , Advanced Functional Materials)

   A synthetic route toward hybrid MoS₂‐based materials that combines the 2D bonding of MoS₂with 3D networking of aliphatic carbon chains is devised, leading to a film with enhanced electrocatalytic activity. The hybrid inorganic–organic thin films are synthesized by combining atomic layer deposition (ALD) with molecular layer deposition (MLD) using the precursors molybdenum hexacarbonyl and 1,2‐ethanedithiol and characterized by in situ Fourier transform infrared spectroscopy, and the resultant material properties are probed by X‐ray photoelectron spectroscopy, Raman spectroscopy, and grazing incidence X‐ray diffraction. The process exhibits a growth rate of 1.3 Å per cycle, with an ALD/MLD temperature window of 155–175 °C. The hybrid films are moderately stable for about a week in ambient conditions, smooth (σ_RMS≈ 5 Å for films 60 Å thick) and uniform, with densities ranging from 2.2–2.5 g cm⁻³. The material is both optically transparent and catalytically active for the hydrogen evolution reaction (HER), with an overpotential (294 mV at −10 mA cm⁻²) superior to that of planar MoS₂. The enhancement in catalytic activity is attributed to the incorporation of organic chains into MoS₂, which induces a morphological change during electrochemical testing that increases surface area and yields high activity HER catalysts without the need for deliberate nanostructuring.

    

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3. Computational Screening of Efficient Single‐Atom Catalysts Based on Graphitic Carbon Nitride (g‐C 3 N 4 ) for Nitrogen Electroreduction

   https://doi.org/10.1002/smtd.201800368  

   Chen, Zhe ; Zhao, Jingxiang ; Cabrera, Carlos R. ; Chen, Zhongfang ( December 2018 , Small Methods)

   The development of low‐cost and efficient electrocatalysts for nitrogen reduction reaction (NRR) at ambient conditions is crucial for NH₃synthesis and provides an alternative to the traditional Harber‐Bosch process. Herein, by means of density functional theory (DFT) computations, the catalytic performance of a series of single metal atoms supported on graphitic carbon nitride (g‐C₃N₄) for NRR is evaluated. Among all the candidates, the Gibbs free energy change of the potential‐determining step for five single‐atom catalysts (SACs), namely Ti, Co, Mo, W, and Pt atoms supported on g‐C₃N₄monolayer, is lower than that on the Ru(0001) stepped surface. In particular, the single tungsten (W) atom anchored on g‐C₃N₄(W@g‐C₃N₄) exhibits the highest catalytic activity toward NRR with a limiting potential of −0.35 V via associative enzymatic pathway, and can well suppress the competing hydrogen evolution reaction. The high NRR activity and selectivity of W@g‐C₃N₄are attributed to its inherent properties, such as significant positive charge and large spin moment on the W atom, excellent electrical conductivity, and moderate adsorption strength with NRR intermediates. This work opens up a new avenue of N₂reduction for renewable energy supplies and helps guide future development of single‐atom catalysts for NRR and other related electrochemical process.

    

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4. Carbon aerogels with atomic dispersion of binary iron–cobalt sites as effective oxygen catalysts for flexible zinc–air batteries

   https://doi.org/10.1039/d0ta04633g  

   Chen, Yang ; Hu, Shengqiang ; Nichols, Forrest ; Bridges, Frank ; Kan, Shuting ; He, Ting ; Zhang, Yi ; Chen, Shaowei ( June 2020 , Journal of Materials Chemistry A)

   null (Ed.)

   Iron single atom catalysts have emerged as one of the most active electrocatalysts towards the oxygen reduction reaction (ORR), but the unsatisfactory durability and limited activity for the oxygen evolution reaction (OER) has hampered their commercial applications in rechargeable metal–air batteries. By contrast, cobalt-based catalysts are known to afford excellent ORR stability and OER activity, due to the weak Fenton reaction and low OER Gibbs free energy. Herein, a bimetal hydrogel template is used to prepare carbon aerogels containing Fe–Co bimetal sites (NCAG/Fe–Co) as bifunctional electrocatalysts towards both ORR and OER, with enhanced activity and stability, as compared to the monometal counterparts. High-resolution transmission electron microscopy, elemental mapping and X-ray photoelectron spectroscopy measurements demonstrate homogeneous distributions of the metal centers within defected carbon lattices by coordination to nitrogen dopants. X-ray absorption spectroscopic measurements, in combination with other results, suggest the formation of FeN 3 and CoN 3 moieties on mutually orthogonal planes with a direct Fe–Co bonding interaction. Electrochemical measurements show that NCAG/Fe–Co delivers a small ORR/OER potential gap of only 0.64 V at the current density of 10 mA cm −2 , 60 mV lower than that (0.70 V) with commercial Pt/C and RuO 2 catalysts. When applied in a flexible Zn–air battery, the dual-metal NCAG/Fe–Co catalyst also shows a remarkable performance, with a high open-circuit voltage of 1.47 V, a maximum power density of 117 mW cm −2 , as well as good rechargeability and flexibility. Results from this study may offer an ingenious protocol in the design and engineering of highly efficient and durable bifunctional electrocatalysts based on dual metal-doped carbons. 

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5. Well-defined surface catalytic sites for solar CO 2 reduction: heterogenized molecular catalysts and single atom catalysts

   https://doi.org/10.1039/D3CC01821K  

   Huang, Peipei ; Shaaban, Ehab ; Ahmad, Esraa ; St. John, Allison ; Jin, Tianqi ; Li, Gonghu ( July 2023 , Chemical Communications)

   Exciting progress has been made in the area of solar fuel generation by CO 2 reduction. New photocatalytic materials containing well-defined surface catalytic sites have emerged in recent years, including heterogenized molecular catalysts and single atom catalysts. This Feature Article summarizes our recent research in this area, together with brief discussions of relevant literature. In our effort to obtain heterogenized molecular catalysts, a diimine-tricarbonyl Re( i ) complex and a tetraaza macrocyclic Co( iii ) compound were covalently attached to different surfaces, and the effects of ligand derivatization and surface characteristics on their structures and photocatalytic activities were investigated. Single atom catalysts combine the advantages of homogeneous and heterogeneous catalysis. A single-site cobalt catalyst was prepared on graphitic carbon nitride, which demonstrated excellent activity in selective CO 2 reduction under visible-light irradiation. Doping carbon nitride with carbon was found to have profound effects on the structure and activity of the single-site cobalt catalyst. Our research achievements are presented to emphasize how spectroscopic techniques, including infrared, UV-visible, electron paramagnetic resonance, and X-ray absorption spectroscopies, could be combined with catalyst synthesis and computation modeling to understand the structures and properties of well-defined surface catalytic sites at the molecular level. This article also highlights challenges and opportunities in the broad context of solar CO 2 reduction. 

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