Browsing by Author "Sun, Zhenyu"

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    Achieving Highly Selective Electrocatalytic CO2 Reduction by Tuning CuO-Sb2O3 Nanocomposites
    (ACS Sustainable Chemistry & Engineering, 2020) Li, Yangmei; Chu, Senlin; Shen, Huidong; Xia, Qineng; Robertson, Alex W.; Masa, Justus; Siddiqui, Umer; Sun, Zhenyu
    The development of highly active and selective electrocatalysts with low cost and earth abundance for electrochemical CO2 reduction (ECR) remains an important area of interest. Here, we report the modification of CuO with other metal (Bi, Sb, Cd, and Zr) oxides to form bimetallic oxide nanocomposite catalysts exhibiting efficient ECR. In particular, CuO-Sb2O3 nanoparticles anchored on carbon black (CB) facilitated ECR selectively to CO at low overpotentials, providing a CO faradaic efficiency (FE) of up to 90.0% at −0.8 V versus reversible hydrogen electrode, in contrast to individual CuO/CB and Sb2O3/CB, which gave rise to CO FEs of less than 31.0%, outperforming many previously reported catalysts. A strong interaction between CuO and Sb2O3 is found, which likely contributes to the enhanced ECR activity.
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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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    High-yield Exfoliation of Graphite in Acrylate Polymers: A stable few-layer graphene nanofluid with enhanced thermal conductivity
    (Carbon, 2013) Sun, Zhenyu; Pöller, Sascha; Masa, Justus; Kilzer, Andreas
    High-yield exfoliation of pristine graphite in low boiling point alcohols was achieved using a set of acrylate polymers resulting in few-layer graphene concentrations of up to ∼4 mg mL−1. The polymer showed superior dispersing capabilities for graphene compared to the best reported dispersants, including the solvent N-methyl-pyrrolidone, the surfactants sodium cholate and sodium taurodeoxycholate, and the polymer polyvinylpyrrolidone. The dispersions were stable regardless of freezing (−26 °C) or heating (70 °C) for 24 h, or dilution with water up to 80% volume ratio over 160 h. The as-obtained nanofluid exhibited an enhancement in thermal conductivity suggesting a great potential in coolant applications.
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    Highly Concentrated Aqueous Dispersions of Graphene Exfoliated by Sodium Taurodeoxycholate: Dispersion Behavior and Potential Application as a Catalyst Support for the Oxygen-Reduction Reaction
    (Chemistry–A European Journal, 2012) Sun, Zhenyu; Masa, Justus; Liu, Zhimin; Schuhmann, Wolfgang; Muhler, Martin
    A high-yielding exfoliation of graphene at high concentrations in aqueous solutions is critical for both fundamental study and future applications. Herein, we demonstrate the formation of stable aqueous dispersions of pristine graphene by using the surfactant sodium taurodeoxycholate under tip sonication at concentrations of up to 7.1 mg mL−1. TEM showed that about 8 % of the graphene flakes consisted of monolayers and 82 % of the flakes consisted of less than five layers. The dispersions were stable regardless of freezing (−20 °C) or heat treatment (80 °C) for 24 h. The concentration could be significantly improved to about 12 mg mL−1 by vacuum-evaporation of the dispersions at ambient temperature. The as-prepared graphene dispersions were readily cast into conductive films and were also processed to prepare Pt/graphene nanocomposites that were used as highly active electrocatalysts for the oxygen-reduction reaction.
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    Stabilization of Cu+ by tuning a CuO–CeO2 interface for selective electrochemical CO2 reduction to ethylene
    (Green Chemistry, 2020) Chu, Senlin; Yan, Xupeng; Choi, Changhyeok; Masa, Justus; Han, Buxing; Jung, Yousung; Sun, Zhenyu
    Electrochemical conversion of carbon dioxide (CO2) into multi-carbon fuels and chemical feedstocks is important but remains challenging. Here, we report the stabilization of Cu+ within a CuO–CeO2 interface for efficient and selective electrocatalytic CO2 reduction to ethylene under ambient conditions. Tuning the CuO/CeO2 interfacial interaction permits dramatic suppression of proton reduction and enhancement of CO2 reduction, with an ethylene faradaic efficiency (FE) as high as 50.0% at −1.1 V (vs. the reversible hydrogen electrode) in 0.1 M KHCO3, in stark contrast to 22.6% over pure CuO immobilized on carbon black (CB). The composite catalyst presents a 2.6-fold improvement in ethylene current compared to that of CuO/CB at similar overpotentials, which also exceeds many recently reported Cu-based materials. The FE of C2H4 remained at over 48.0% even after 9 h of continuous polarization. The Cu+ species are believed to be the adsorption as well as active sites for the activation of CO2 molecules, which remain almost unchanged after 1 h of electrolysis. Further density functional theory calculations demonstrate the preferred formation of Cu+ at the CuO–CeO2 interface. This work provides a simple avenue to convert CO2 into high-value hydrocarbons by rational stabilization of Cu+ species.