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  • 1.
    Wang, Wei
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Lanzhou Jiaotong University, China.
    Chen, Keyu
    Sun, Yan
    Zhou, Shiqi
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Zhang, Miao
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Yuan, Jiayin
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Mesoporous Ni-N-C as an efficient electrocatalyst for reduction of CO2 into CO in a flow cell2022In: Applied Materials Today, ISSN 2352-9407, Vol. 29, article id 101619Article in journal (Refereed)
    Abstract [en]

    Recently, nitrogen-doped porous carbon materials containing non-precious metals (termed “M-N-C”) have formed a group of functional materials to replace precious metal-based catalysts for electrochemical CO2 reduction reaction. Here, a series of mesoporous Ni-N-C electrocatalysts (termed “mp-Ni-N-Cs”) were prepared via a gel-template method, and could effectively reduce CO2 into CO in a flow cell. The result in gas sorption tests exhibited a typical mesoporous structure, which would bring both sufficient exposed active sites and convenient mass transfer channels. Electrochemical tests showed excellent performance at an applied potential of -1.3 V (vs. RHE), e.g., a CO Faradaic efficiency (FECO) of 95.85 %, and a CO reduction current (jCO) of -21.29 mA cm−2. Significantly, its FECO exceeded 93 % in a wide range of potentials from -1.0 to -1.5 V, showing great tolerance to fluctuation in potential. The mp-Ni-N-C electrocatalysts have satisfactory features in terms of catalytic activity, facile preparation, and economic feasibility, and will offer a valuable reference for next exploration of cost-effective electrocatalysts for CO2 conversion.

  • 2. Wang, Wei
    et al.
    Han, Juan
    Sun, Yan
    Zhang, Miao
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Zhou, Shiqi
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Zhao, Kai
    Yuan, Jiayin
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Metal-Free SeBN Ternary-Doped Porous Carbon as Efficient Electrocatalysts for CO2 Reduction Reaction2022In: ACS Applied Energy Materials, E-ISSN 2574-0962, Vol. 5, no 9, p. 10518-10525Article in journal (Refereed)
    Abstract [en]

    Cost-effective heteroatom-doped porous carbons are considered promising electrocatalysts for CO2 reduction reaction (CO2RR). Traditionally porous carbons with N doping or N/X codoping (X denotes the second type of heteroatom) have been widely studied, leaving ternary doping a much less studied yet exciting topic to be explored. Herein, a series of electrocatalysts based on metal-free Se, B, and N ternary-doped porous carbons (termed “SeBN-Cs”) were synthesized and tested as metal-free electrocatalysts in CO2RR. Our study indicates that the major product of CO2RR on the SeBN-C electrocatalysts was CO with a small fraction (<5%) of H2 as the byproduct. The optimal electrocatalyst sample SeBN-C-1100 prepared at 1100 °C exhibits a high CO selectivity with a Faradaic efficiency of CO reaching 95.2%. After 10 h of continuous electrolysis operation, the Faradaic efficiency and the current density are maintained high at 97.6 and 84.7% of the initial values, respectively, indicative of a long-term operational stability. This study provides an excellent reference to deepen our understanding of the properties and functions of multi-heteroatom-doped porous carbon electrocatalysts in CO2RR. 

  • 3.
    Zhou, Shiqi
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Multiscale interfacial engineering of heterogeneous electrocatalysts: From structural design to mechanistic study2024Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In a typical heterogeneous electrocatalytic reaction, for the given active sites, the electronic structure plays a determining role in electron transfer between the active sites and reactant molecules, which impacts the reaction efficiency. Besides the electronic properties of the electrocatalysts, the reaction interface at which the charge transfer occurs plays an important role in the reaction kinetics. Moreover, the accessibility of the active sites to the reactant molecules also affects the reaction efficiency. However, a well-balanced effective strategy for electronic structure optimization that improves not only the activity but also stability and cost-effectiveness is needed. Besides, a robust model specifically tailored to investigate the kinetics of the electrocatalytic reaction is required to exclude the interference of thermodynamic factors. A feasible characterization technique for probing the complex interfacial process is also required.

     

    To address these remaining challenges in the three aspects above, this thesis proposed the strategies to optimize the electrocatalytic reaction processes as follows:

     

    (1) Tuning the electronic structure of the active sites by engineering coordination environment and introducing strain effect. Specifically, Ni single atom was constructed to engineer the coordination environment, and the electrocatalytic performance with the tuned electronic structure was examined towards hydrazine oxidation reaction. The strain effect was created by introducing Cu single atom to BiOCl substrate, and the optimized electronic structure was investigated;

    (2) Optimizing the interfacial HER kinetics targeted by proposing a specific Pt model catalyst with a channel-opening modifier. The interfacial water structure was studied by in situ surface-enhanced Raman technique, and the role of this promoting modifier was elucidated by ab initio molecular dynamic simulation;

    (3) Improving the local concentration of CO2 for electrochemical CO2 reduction reaction with a poly(ionic liquid) modifier, with Au as the model catalyst and the targeted characterization techniques.

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  • 4.
    Zhou, Shiqi
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Yuan, Jiayin
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Engineering interfacial hydrogen-bond network via cage-enabled soft confinement of Pt for facilitated hydrogen evolution kineticsManuscript (preprint) (Other academic)
    Abstract [en]

    The sluggish HER kinetics under alkaline conditions largely limit the development of alkaline water electrolysis. Decades of efforts have been reported to elucidate the origin of the pH dependence of HER kinetics and facilitate the alkaline HER kinetics. Apart from the widely concerned thermodynamic factors, the electrode process also depends unignorably on the kinetics of the electrochemical interface. Herein, we presented the facilitated HER kinetics by introducing porous amine cage-enabled confinement to Ptcatalyst to engineer the interface between the Pt surface and the aqueous electrolyte. In situ electrochemical surface-enhanced Raman spectra (SERS) measurements and ab initio molecular dynamics (AIMD) simulation jointly unveiled the fundamental interfacial interaction between water and cage that its -NH- moiety largely reduces the rigidity of the net of interfacial water H-bonds at negative HER potentials, which makes the net flexible enough to reorganize for better charge transfer. Our in-depth investigation pinpointed that the -NH- moiety acted as a proton pump and generated hydroxide transfer by forming and breaking H-bonds with interfacial water, refreshing the reactive water layer on the Pt surface. Our results address the crucial role of controllable interfacial kinetics during electrocatalytic reactions, and our strategy of establishing a soft-confining interfacial regulator offers a promising roadmap for manipulating electrocatalytic interfacial kinetics.

  • 5.
    Zhou, Shiqi
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Yuan, Jiayin
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Singly Dispersed Copper Atoms with Compressive Residual Strain for Superior Photocatalytic Diluted CO2 ReductionManuscript (preprint) (Other academic)
    Abstract [en]

    Solar-driven diluted CO2 reduction is an alternative way to realize carbon neutrality, although promoting the photo-reactivity and selectivity in low CO2 contents remains a great challenge. Herein, an atomically dispersed Cu catalyst in a compressive strained BiOCl substrate (Cu1-BOC-CRS) is identified as a promising photocatalyst for diluted CO2 reduction reaction, capable of producing CO without any sacrificial agents or sensitizers. The single Cu atoms and the local surface strain facilitate CO2 adsorption, resulting in impressive CO formation rates of 122 and 99 μmol g-1 h-1 respectively under pure and diluted CO2 conditions. Experimental investigations revealed that the occupation of single Cu atoms in the BiOCl extends the light absorbance and charge transfer, which in turn integrates the surface CO2 capture and conversion. Moreover, the compressive strain provides an extra low-energy route towards CO2-to-CO conversion, offering valuable insights for the future design of highly efficient photocatalysts for diluted CO2 reduction.

  • 6.
    Zhou, Shiqi
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Yuan, Jiayin
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Tahavori, Elnaz
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    CO2-philic poly(ionic liquid)-assisted local enrichment strategy for enhancedelectrochemical CO2 reductionManuscript (preprint) (Other academic)
    Abstract [en]

    Electrochemical CO2 reduction reaction (ECO2RR) to produce valuable chemicals and fuels is a promising way to make use of excessive CO2 as one of the major green-house gases debatably responsible for climate change. The chemically inert feature of CO2 molecules makes the first-step elementary reaction with one electron reduction challenging in thermodynamics, leading to a high overpotential for this step and the overall ECO2RR as well. Herein, we reported the successful fabrication of CO2-philic PIL-modified Au model catalyst with enhanced ECO2RR performance by a local CO2 enrichment strategy. The modified gas diffusion electrode exhibited ~ 100% Faradaic efficiency for CO2-to-CO conversion (FECO) in a wide potential window of -0.2 ~ -1.0 V (versus reversible hydrogen electrode. RHE) with pure CO2 feeding, and notablymaintained the FECO > 90% even at a low CO2 concentration of 20 % vol..

  • 7.
    Zhou, Shiqi
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Zhao, Yunxuan
    Shi, Run
    Wang, Yucheng
    Ashok, Anumol
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Héraly, Frédéric
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Zhang, Tierui
    Yuan, Jiayin
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Vacancy-Rich MXene-Immobilized Ni Single Atoms as a High-Performance Electrocatalyst for the Hydrazine Oxidation Reaction2022In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 34, no 36, article id 2204388Article in journal (Refereed)
    Abstract [en]

    Single-atom catalysts (SACs), on account of their outstanding catalytic potential, are currently emerging as high-performance materials in the field of heterogeneous catalysis. Constructing a strong interaction between the single atom and its supporting matrix plays a pivotal role. Herein, Ti3C2Tx-MXene-supported Ni SACs are reported by using a self-reduction strategy via the assistance of rich Ti vacancies on the Ti3C2Tx MXene surface, which act as the trap and anchor sites for individual Ni atoms. The constructed Ni SACs supported by the Ti3C2Tx MXene (Ni SACs/Ti3C2Tx ) show an ultralow onset potential of −0.03 V (vs reversible hydrogen electrode (RHE)) and an exceptional operational stability toward the hydrazine oxidation reaction (HzOR). Density functional theory calculations suggest a strong coupling of the Ni single atoms and their surrounding C atoms, which optimizes the electronic density of states, increasing the adsorption energy and decreasing the reaction activation energy, thus boosting the electrochemical activity. The results presented here will encourage a wider pursuit of 2D-materials-supported SACs designed by a vacancy-trapping strategy. 

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