Sung Yul Lim

Light-guided electrodeposition of non-noble catalyst patterns for photoelectrochemical hydrogen evolution

Hydrogen is in the lime light as a carbon-free alternative energy source due to its high energy conversion efficiency. Solar-driven water splitting is one of the most promising methods for renewable hydrogen production. However, commercialization of a photoelectrochemical hydrogen production system remains a great challenge. One of the emerging concerns is the development of an inexpensive and transparent catalyst, which does not obstruct the light pathways to the semiconductor electrode. Here we report a non-noble metal electrocatalyst for hydrogen evolution, Ni-Mo, which is directly patterned on amorphous Si (a-Si) by light-guided spatially selective electrodeposition without consecutive photolithography processes. A light pattern is illuminated onto the a-Si using a digital micromirror device to commence the photoelectrochemical deposition. The catalyst patterned by the proposed method not only admits sufficient light to a-Si but also enables long distance carrier transport along the inversion layer, as previously observed in crystalline Si (c-Si) photocathodes. This new electrodeposition method enables mask-free patterning on a-Si and is expected to expedite a lower cost, more efficient, and self-biasing integrated photoelectrochemical water-splitting device.

Nonfaradaic Nanoporous Electrochemistry for Conductometry at High Electrolyte Concentration

Nanoporous electrified surfaces create a unique nonfaradaic electrochemical behavior that is sensitively influenced by pore size, morphology, ionic strength, and electric field modulation. Here, we report the contributions of ion concentration and applied ac frequency to the electrode impedance through an electrical double layer overlap and ion transport along the nanopores. Nanoporous Pt with uniform pore size and geometry (L2-ePt) responded more sensitively to conductivity changes in aqueous solutions than Pt black with poor uniformity despite similar real surface areas and enabled the previously difficult quantitative conductometry measurements at high electrolyte concentrations. The nanopores of L2-ePt were more effective in reducing the electrode impedance and exhibited superior linear responses to not only flat Pt but also Pt black, leading to successful conductometric detection in ion chromatography without ion suppressors and at high ionic strengths.

Gold Microshell Tip for In Situ Electrochemical Raman Spectroscopy

Tip fabrication by a new strategy is proposed for simultaneous acquisition of electrochemical (EC) signals from an ultramicroelectrode and spectroscopic information from surface-enhanced Raman scattering (SERS). The EC-SERS tip is prepared by carefully tuning a SERS-active gold microshell to maximize Raman scattering, mechanically attaching it to the end of a micropipet, and electrically connecting it to a ruthenium inner layer through electroless deposition.

Chemically Deposited Cobalt-Based Oxygen-Evolution Electrocatalysts on DOPA-Displaying Viruses

Filamentous bacteriophages were engineered to display 3,4‐dihydroxy‐l‐phenylalanine (DOPA) onto which a cobalt oxide based oxygen‐evolution catalyst (Co‐OEC) spontaneously deposited at room temperature. Relative to the electrodeposited Co‐OEC, the catalyst formed on the virus exhibited improved durability and current density in a small overpotential region, as well as decreased oxidation states for the formation of Co(OH)2, as confirmed by electrochemical and X‐ray photoelectron spectroscopy analysis. Chemically deposited Co(OH)2 on the virus was oxidized to CoOOH during the water‐oxidation process. Thus, the DOPA‐displaying virus illustrates the affordability of a genetically engineered bacteriophage as a molecular support that can improve the catalytic performance of inorganic materials without any additional electrical energy.