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1. Accelerating CO 2 Electroreduction to CO Over Pd Single‐Atom Catalyst

   https://doi.org/10.1002/adfm.202000407  

   He, Qun ; Lee, Ji Hoon ; Liu, Daobin ; Liu, Yumeng ; Lin, Zhexi ; Xie, Zhenhua ; Hwang, Sooyeon ; Kattel, Shyam ; Song, Li ; Chen, Jingguang G. ( March 2020 , Advanced Functional Materials)

   The electrochemical conversion of carbon dioxide (CO₂) into value‐added chemicals is regarded as one of the promising routes to mitigate CO₂emission. A nitrogen‐doped carbon‐supported palladium (Pd) single‐atom catalyst that can catalyze CO₂into CO with far higher mass activity than its Pd nanoparticle counterpart, for example, 373.0 and 28.5 mA mg⁻¹_Pd, respectively, at −0.8 V versus reversible hydrogen electrode, is reported. A combination of in situ X‐ray characterization and density functional theory (DFT) calculation reveals that the PdN₄site is the most likely active center for CO production without the formation of palladium hydride (PdH), which is essential for typical Pd nanoparticle catalysts. Furthermore, the well‐dispersed PdN₄single‐atom site facilitates the stabilization of the adsorbed CO₂intermediate, thereby enhancing electrocatalytic CO₂reduction capability at low overpotentials. This work provides important insights into the structure‐activity relationship for single‐atom based electrocatalysts.

    

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2. Dual functions of CO 2 molecular activation and 4f levels as electron transport bridges in erbium single atom composite photocatalysts therefore enhancing visible-light photoactivities

   https://doi.org/10.1039/D1TA02926F  

   Chen, Qiuyu ; Gao, Guoyang ; Zhang, Yanzhou ; li, Yini ; Zhu, Hongyang ; Zhu, Peifen ; Qu, Yang ; Wang, Guofeng ; Qin, Weiping ( July 2021 , Journal of Materials Chemistry A)

   Only when the interfacial charge separation is enhanced and the CO 2 activation is improved, can the heterojunction nanocomposite photocatalyst be brought into full play for the CO 2 reduction reaction (CO 2 RR). Here, Er 3+ single atom composite photocatalysts were successfully constructed based on both the special role of Er 3+ single atoms and the special advantages of the SrTiO 3 :Er 3+ /g-C 3 N 4 heterojunction in the field of photocatalysis for the first time. As we expected, the SrTiO 3 :Er 3+ /g-C 3 N 4 (22.35 and 16.90 μmol g −1 h −1 for CO and CH 4 ) exhibits about 5 times enhancement in visible-light photocatalytic activity compared to pure g-C 3 N 4 (4.60 and 3.40 μmol g −1 h −1 for CO and CH 4 ). In particular, the photocatalytic performance of SrTiO 3 :Er 3+ /g-C 3 N 4 is more than three times higher than that of SrTiO 3 /g-C 3 N 4 . From Er 3+ fluorescence quenching measurements, photoelectrochemical studies, transient PL studies and DFT calculations, it is verified that a small fraction of surface doping of Er 3+ formed Er single-atoms on SrTiO 3 building an energy transfer bridge between the interface of SrTiO 3 and g-C 3 N 4 , resulting in enhanced interfacial charge separation. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (AC HAADF-STEM) and adsorption energy calculations demonstrated that the exposed Er single-atoms outside the interface on SrTiO 3 preferentially activate the adsorbed CO 2 , leading to the high photoactivity for the CO 2 RR. A novel enhanced photocatalytic mechanism was proposed, in which Er single-atoms play dual roles of an energy transfer bridge and activating CO 2 to promote charge separation. This provides new insights and feasible routes to develop highly efficient photocatalytic materials by engineering rare-earth single-atom doping. 

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3. Cobalt telluride electrocatalyst for selective electroreduction of CO2 to value-added chemicals

   https://doi.org/10.1007/s40243-022-00211-6  

   Saxena, Apurv ; Singh, Harish ; Nath, Manashi ( July 2022 , Materials for Renewable and Sustainable Energy)

   Recent emphasis on carbon dioxide utilization has necessitated the exploration of different catalyst compositions other than copper-based systems that can significantly improve the activity and selectivity towards specific CO₂ reduction products at low applied potential. In this study, a binary CoTe has been reported as an efficient electrocatalyst for CO₂reduction in aqueous medium under ambient conditions at neutral pH. CoTe showed high Faradaic efficiency and selectivity of 86.83 and 75%, respectively, for acetic acid at very low potential of − 0.25 V vs RHE. More intriguingly, C1 products like formic acid was formed preferentially at slightly higher applied potential achieving high formation rate of 547.24 μmol cm⁻² h⁻¹ at − 1.1 V vs RHE. CoTe showed better CO2RR activity when compared with Co₃O₄, which can be attributed to the enhanced electrochemical activity of the catalytically active transition metal center as well as improved intermediate adsorption on the catalyst surface. While reduced anion electronegativity and improved lattice covalency in tellurides enhance the electrochemical activity of Co, high d-electron density improves the intermediate CO adsorption on the catalyst site leading to CO₂reduction at lower applied potential and high selectivity for C₂products. CoTe also shows stable CO2RR catalytic activity for 50 h and low Tafel slope (50.3 mV dec^–1) indicating faster reaction kinetics and robust functionality. Selective formation of value-added C₂products with low energy expense can make these catalysts potentially viable for integration with other CO₂capture technologies thereby, helping to close the carbon loop.

    

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4. Ni 2 P‐Modified Ta 3 N 5 and TaON for Photocatalytic Nitrate Reduction

   https://doi.org/10.1002/cnma.202000174  

   Wei, Lin ; Adamson, Marquix A. S. ; Vela, Javier ( May 2020 , ChemNanoMat)

   Self‐sustaining photocatalytic NO₃⁻reduction systems could become ideal NO₃⁻removal methods. Developing an efficient, highly active photocatalyst is the key to the photocatalytic reduction of NO₃⁻. In this work, we present the synthesis of Ni₂P‐modified Ta₃N₅(Ni₂P/Ta₃N₅), TaON (Ni₂P/TaON), and TiO₂(Ni₂P/TiO₂). Starting with a 2 mM (28 g/mL NO₃⁻−N) aqueous solution of NO₃⁻, as made Ni₂P/Ta₃N₅and Ni₂P/TaON display as high as 79% and 61% NO₃⁻conversion under 419 nm light within 12 h, which correspond to reaction rates per gram of 196 μmol g⁻¹ h⁻¹and 153 μmol g⁻¹ h⁻¹, respectively, and apparent quantum yields of 3–4%. Compared to 24% NO₃⁻conversion in Ni₂P/TiO₂, Ni₂P/Ta₃N₅and Ni₂P/TaON exhibit higher activities due to the visible light active semiconductor (SC) substrates Ta₃N₅and TaON. We also discuss two possible electron migration pathways in Ni₂P/semiconductor heterostructures. Our experimental results suggest one dominant electron migration pathway in these materials, namely: Photo‐generated electrons migrate from the semiconductor to co‐catalyst Ni₂P, and upshift its Fermi level. The higher Fermi level provides greater driving force and allows NO₃⁻reduction to occur on the Ni₂P surface.

    

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5. Methanol tolerance of atomically dispersed single metal site catalysts: mechanistic understanding and high-performance direct methanol fuel cells

   https://doi.org/10.1039/d0ee01968b  

   Shi, Qiurong ; He, Yanghua ; Bai, Xiaowan ; Wang, Maoyu ; Cullen, David A. ; Lucero, Macros ; Zhao, Xunhua ; More, Karren L. ; Zhou, Hua ; Feng, Zhenxing ; et al ( January 2020 , Energy & Environmental Science)

   Proton-exchange membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs) are promising power sources from portable electronic devices to vehicles. The high-cost issue of these low-temperature fuel cells can be primarily addressed by using platinum-group metal (PGM)-free oxygen reduction reaction (ORR) catalysts, in particular atomically dispersed metal–nitrogen–carbon (M–N–C, M = Fe, Co, Mn). Furthermore, a significant advantage of M–N–C catalysts is their superior methanol tolerance over Pt, which can mitigate the methanol cross-over effect and offer great potential of using a higher concentration of methanol in DMFCs. Here, we investigated the ORR catalytic properties of M–N–C catalysts in methanol-containing acidic electrolytes via experiments and density functional theory (DFT) calculations. FeN 4 sites demonstrated the highest methanol tolerance ability when compared to metal-free pyridinic N, CoN 4 , and MnN 4 active sites. The methanol adsorption on MN 4 sites is even strengthened when electrode potentials are applied during the ORR. The negative influence of methanol adsorption becomes significant for methanol concentrations higher than 2.0 M. However, the methanol adsorption does not affect the 4e − ORR pathway or chemically destroy the FeN 4 sites. The understanding of the methanol-induced ORR activity loss guides the design of promising M–N–C cathode catalyst in DMFCs. Accordingly, we developed a dual-metal site Fe/Co–N–C catalyst through a combined chemical-doping and adsorption strategy. Instead of generating a possible synergistic effect, the introduced Co atoms in the first doping step act as “scissors” for Zn removal in metal–organic frameworks (MOFs), which is crucial for modifying the porosity of the catalyst and providing more defects for stabilizing the active FeN 4 sites generated in the second adsorption step. The Fe/Co–N–C catalyst significantly improved the ORR catalytic activity and delivered remarkably enhanced peak power densities ( i.e. , 502 and 135 mW cm −2 ) under H 2 –air and methanol–air conditions, respectively, representing the best performance for both types of fuel cells. Notably, the fundamental understanding of methanol tolerance, along with the encouraging DMFC performance, will open an avenue for the potential application of atomically dispersed M–N–C catalysts in other direct alcohol or ammonia fuel cells. 

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