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에 해당하는 백금 나노구조에서 가장 우수한 촉매 활성이 관찰되었다. 전하량에 따른 표면적의 변화보다 형성된 구조적 특이성과 결정면이 촉매 활성에 많은 영향을 미쳤다. 세밀한 백금 나노구조의 변화에 따른 전기화학적 촉매 활성 변화에 관한 본 연구결과는 보다 우수한 촉매 시스템을 고안하는 연구에 도움이될 것이다.Abstract : We report on the electrocatalytic activities at Pt nanostructure surfaces electrode-posited with different deposition charges on indium tin oxide electrodes for oxygen reductionand methanol oxidation reactions. The surface properties of Pt nanostructures depending ondeposition charges were characterized by scanning electron microscopy, electrochemical sur-face area measurement, X-ray diffraction, and CO stripping analysis, which were correlatedto the electrocatalytic activities. Pt nanostructures with deposition charge of 0.03 C exhibitedthe highest electrocatalytic activity for oxygen reduction and methanol oxidation. The sharpsites of Pt nanostructure and the presence of highly active facet play a key role, whereasthe electrochemical surface area does not significantly affect the electrocatalytic activity. Theresults obtained in this work with regard to the dependence of electrocatalytic activity onthe variation of the Pt nanostructures will give insights into the development of advancedelectrocatalytic systems.Keywords : Electrodeposition, Dendritic Pt, Oxygen reduction, Methanol oxidation

전기화학적 석출에 의해 Ag-Au 합금층을 전극표면에 형성한 후 진한 질산으로 Ag만을 녹여내는 기법으로 나노다공성 금 (nanoporous gold, NPG) 구조를 만들어 전기화학적 산소환원에 대한 촉매현상을 관찰하였다. 석출과정의 전구체의 농도비를 달리하였을 때 나타나는 NPG 표면구조의 변화를 주사전자현미경으로 관찰하고 전기화학적 표면적을 측정하였다. 전기화학적 산소환원 촉매 효율은 NPG 표면의 구조에 따라 달라졌는데, Ag/Au 비율이 2.0에 해당하는 NPG 구조에서 가장 우수한 촉매 현상이 관찰 되었다. 표면구조의 변화에 따른 촉매 활성 변화에서 다공성 구조의 역할이 매우 큰 기여를 하는 반면 표면적의 변화는 큰 영향을 미치지 않았다. 최적 조건의 NPG 구조상의 전기화학적 산소환원 과정의 메커니즘을 회전원판전극 실험을 통해 관찰하였는데, 산성 조건에서 NPG 전극에서 전기화학적 산소환원은 과산화수소를 거쳐 물이 생성되는 2-단계 4-전자 환원 메커니즘으로 진행되었고 염기성 조건에서는 산소가 4개의 전자 전달을 통해 물로 직접적으로 환원 되었다. Abstract : We investigate the electrocatalytic activities for oxygen reduction at nanoporousgold (NPG) surfaces fabricated by selective dissolution of Ag from electrodeposited Ag-Au lay-ers on electrode surfaces. The structure of NPG was controlled by changing the concentrationratios of precursor metal complexes during the electrodeposition of Ag-Au layers and the cor-responding surface morphology and surface area was examined. NPG structures with Ag/Auratio of 2.0 exhibited the highest electrocatalytic activity for oxygen reduction, where the nan-oporous structure plays a key role, but the surface area does not affect on the electrocatalyticactivity. The mechanism of electroreduction of oxygen was investigated by rotating disk elec-trode techniques. In acidic media, oxygen was first reduced to hydrogen peroxide followed byfurther reduction to water through 2-step 4-electron mechanism, whereas the oxygen wasreduced directly to water by 4-electron mechanism in basic media.Keywords : Nanoporous gold, Electrocatalysis, Oxygen reduction, Rotating disk electrode

The effect of polyoxometalate monolayers on the electrodeposition of Au nanoparticles (AuNPs) on glassy carbon (GC) surfaces was examined by electrochemical and scanning electron microscope techniques. The presence of -layers resulted in average particle sizes of ca. 60 nm, which is larger than AuNPs deposited on bare GC surfaces. AuNPs electrodeposited on -modified GC surfaces for 20 s exhibited the best electrocatalytic activity for oxygen reduction. This system exhibited similar or slightly better efficiency for oxygen reduction than a bare Au electrode. Rotating disk electrode experiments were also performed and revealed that the catalytic reduction of oxygen on AuNPs deposited on -modified GC electrodes is a two-electron process.