Heejong Shin

Large-Scale Synthesis of Carbon-Shell-Coated FeP Nanoparticles for Robust Hydrogen Evolution Reaction Electrocatalyst

A highly active and stable non-Pt electrocatalyst for hydrogen production has been pursued for a long time as an inexpensive alternative to Pt-based catalysts. Herein, we report a simple and effective approach to prepare high-performance iron phosphide (FeP) nanoparticle electrocatalysts using iron oxide nanoparticles as a precursor. A single-step heating procedure of polydopamine-coated iron oxide nanoparticles leads to both carbonization of polydopamine coating to the carbon shell and phosphidation of iron oxide to FeP, simultaneously. Carbon-shell-coated FeP nanoparticles show a low overpotential of 71 mV at 10 mA cm-2, which is comparable to that of a commercial Pt catalyst, and remarkable long-term durability under acidic conditions for up to 10 000 cycles with negligible activity loss. The effect of carbon shell protection was investigated both theoretically and experimentally. A density functional theory reveals that deterioration of catalytic activity of FeP is caused by surface oxidation. Extended X-ray absorption fine structure analysis combined with electrochemical test shows that carbon shell coating prevents FeP nanoparticles from oxidation, making them highly stable under hydrogen evolution reaction operation conditions. Furthermore, we demonstrate that our synthetic method is suitable for mass production, which is highly desirable for large-scale hydrogen production.

Electrochemically Synthesized Nanoporous Molybdenum Carbide as a Durable Electrocatalyst for Hydrogen Evolution Reaction

Abstract Demands for sustainable production of hydrogen are rapidly increasing because of environmental considerations for fossil fuel consumption and development of fuel cell technologies. Thus, the development of high‐performance and economical catalysts has been extensively investigated. In this study, a nanoporous Mo carbide electrode is prepared using a top‐down electrochemical process and it is applied as an electrocatalyst for the hydrogen evolution reaction (HER). Anodic oxidation of Mo foil followed by heat treatment in a carbon monoxide (CO) atmosphere forms a nanostructured Mo carbide with excellent interconnections, and these structural characteristics lead to high activity and durability when applied to the HER. Additionally, characteristic behavior of Mo is observed; metallic Mo nanosheets form during electrochemical anodization by exfoliation along the (110) planes. These nanosheets are viable for chemical modification, indicating their feasibility in various applications. Moreover, the role of carbon shells is investigated on the surface of the electrocatalysts, whereby it is suggested that carbon shells serve as a mechanical barrier against the oxidative degradation of catalysts that accompanies unavoidable volume expansion.

Tailoring the porosity of MOF-derived N-doped carbon electrocatalysts for highly efficient solar energy conversion

Metal–organic framework (MOF)-derived carbon materials have been widely used as catalysts for a variety of electrochemical energy applications, and thermally carbonized zinc-2-methylimidazole (ZIF-8) has shown particularly high performance owing to its microporous structure with a large surface area. However, in the presence of bulky chemical species, such as triiodide, in mesoscopic dye-sensitized solar cells (DSCs), the small pore size of carbonized ZIF-8 causes a significant limitation in mass transfer and consequentially results in a poor performance. To resolve this problem, we herein report a simple strategy to enlarge the pore sizes of ZIF-8-derived carbon by increasing the dwelling time of Zn in ZIF-8 during the thermal carbonization process. A thin and uniform polydopamine shell introduced on the surface of ZIF-8, with the aim of retarding the escape of vaporized Zn species, leads to a dramatic increase in pore sizes, from the micropore to mesopore range. The porosity-tailored carbonized ZIF-8 manifests an excellent electrocatalytic performance in triiodide reduction, and when it was applied as the counter electrode of DSCs, an energy conversion efficiency of up to 9.03% is achievable, which is not only superior to that of the Pt-based counterpart but also among the highest performances of DSCs employing carbonaceous electrocatalysts.