|Understanding Mechanism of Electrochemical Water Oxidation|
: 91 : 2017.11.16 10:39
|일시 : 2017.11.08 17:00|
|소속 : 서울대학교 신소재공학과|
|발표자 : 남기태|
|장소 : RA204|
Water splitting is regarded as a promising step towards environmentally sustainable energy schemes because electrolysis produces only hydrogen and oxygen, without any by-products. The oxygen evolution reaction (OER), an anodic half-cell reaction, requires extremely high overpotential due to its slow reaction kinetics. In nature, there exists a water oxidation complex (WOC) in photosystem II (PSII) comprised of the Mn and Ca elements. The WOC in PSII, in the form of a cubical Mn4CaO5 cluster, efficiently catalyzes water oxidation with extremely low overpotential value (~160 mV) and a high turnover frequency (TOF) number (~25,000 mmolO2 mol-1Mn s-1).
We first identified a new crystal structure, Mn3(PO4)2-3H2O, and demonstrated its superior catalytic performance at neutral pH. We revealed that structural flexibility can stabilize Jahn-Teller distorted Mn(III), and thus facilitate Mn redox during catalysis. Additionally, a new pyrophosphate based Mn compound, Li2MnP2O7 was studied. We verified the influence of Mn valency and asymmetric geometry on water oxidation catalysis using Li2MnP2O7 and its derivatives.
Specific questions that our group intensively focus for the further applications include 1) how we can translate the underlying principles in Mn4CaO5 cluster into the synthetic heterogeneous catalysts and 2) how we can mimic the redox molecule involved biological dark reaction for the CO2 reduction. Toward this vision, we have been developing a new catalytic platform based on sub-10 nm uniform nanoparticles to bridge the gap between atomically defined biological catalysts or their metalloenzyme counterparts and the scalable, electrode depositable heterogeneous catalysts. In this approach, the local atomic geometry is controlled by the nitrogen containing graphitic carbon and the heterogeneous atom doping, that enhance the catalytic activity and selectivity. Additional surface modification by the specific ligand allows for the atomic scale tunability to realize the unique electronic hybridization.