Browsing by Author "Qiu, Jieshan"

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    Electrochemical Ammonia Synthesis: Mechanistic Understanding and Catalyst Design
    (Chem,, 2021) Shen, Huidong; Choi, Changhyeok; Masa, Justus; Qiu, Jieshan; Jung, Yousung; Sun, Zhenyu
    NH3 production is dependent on the century-old Haber-Bosch process, which is energy and capital intensive and relies on H2 from steam reforming, hence, contributing to greenhouse gas emissions. Electrochemical NH3 synthesis can be realized by reaction of N2 and a proton source under mild conditions powered by renewable electricity, which offers a promising carbon-neutral and sustainable strategy. However, N2 has remarkable thermodynamic stability and requires high energy to be activated. Implementation of this “clean” NH3 synthesis route therefore still requires significant enhancement in energy efficiency, conversion rate, and durability, which is only achievable through the design of efficient electrocatalysts. This article provides a timely theoretical and experimental overview of recent advances in the electrocatalytic conversion of N2 to NH3 underlining the development of novel electrocatalysts. Advances of in situ and operando studies for mechanistic understanding of the reaction and the main challenges and strategies for improving electrocatalytic N2 reduction are highlighted.
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    Highly Stable Two-Dimensional Bismuth Metal-Organic Frameworks for Efficient Electrochemical Reduction of CO2
    (Applied Catalysis B: Environmental, 2020) Li, Fang; Gu, Geun Ho; Choi, Changhyeok; Masa, Justus; Mukerjee, Sanjeev; Jung, Yousung; Qiu, Jieshan
    We report a unique 2D bismuth metal-organic framework (Bi-MOF) that possesses permanent accessible porosity for efficient electrochemical CO2 reduction (ECR) to HCOOH. The 2D open-framework structure with helical Bi-O rods bridged by tritopic carboxylate ligands exhibits a remarkable Faradaic efficiency for HCOOH formation over a broad potential window, reaching 92.2 % at ∼ –0.9 V (vs. reversible hydrogen electrode, RHE) with excellent durability over 30 h. The mass-specific HCOOH partial current density is up to 41.0 mA mgBi−1, exceeding 4 times higher than that of commercial Bi2O3 and Bi sheets at ∼ –1.1 V (vs. RHE). Operando and ex-situ X-ray absorption fine structure spectroscopy revealed a structural feature associated with Bi-MOF to preserve Bi(3+) during and after long-term ECR. Theoretical calculations further showed that the crystallographically channels with abundant Bi active sites in the MOF structure favor the formation of *HCOO while suppressing the side-reaction of hydrogen evolution, thereby leading to the high selectivity for HCOOH.