成果報告書詳細
管理番号20090000000620
タイトル*平成20年度中間年報 固体高分子形燃料電池実用化戦略的技術開発 次世代技術開発 白金代替触媒材料の開発にむけた大規模量子化学計算による触媒構造・電子状態解析
公開日2010/3/13
報告書年度2008 - 2008
委託先名三菱重工業株式会社 国立大学法人東京大学物性研究所
プロジェクト番号P05011
部署名燃料電池・水素技術開発部 燃料電池グループ
和文要約以下本編抜粋:1.研究成果の内容及び成果等 本年度は、固体高分子型燃料電池(PEMFC)のカソード(正極)反応 O2 + 4H+ + 4e- → 2H2O (1)に対して密度汎関数法(DFT)に基づいた第一原理計算による原子レベルからの物質シミュレーションを行い、なぜ白金触媒で酸素還元反応が効率よく進行するのかという電気化学において根源的な問いへの一つの回答を行い、仮説的な非白金系触媒材料での酸素分子還元作用の有無や有効性を明らかにすることを目指して研究を行った。
英文要約Title: Strategic Development of PEFC Technologies for Practical Application Development of Technology for Next-generation Fuel Cells 07000628-0
(research theme) Large-scale quantum chemical computational approach to electronic and atomic structures of catalysis --- for the possibility of non-platinum-based catalyst (FY2007-FY2009) FY2008 Annual Report
We examined how the oxygen reduction at electrode of polymer
electrolyte fuel cell proceeds using the first principle molecule
dynamics simulation. The electrode model constituted of an adsorption
oxygen molecule, water molecules, a hydronium ion and the chloride
ion, which was introduced as the counter charge of the hydronium ion.
At first we examined the Pt metal electrode and clarified the
elementary reaction process where an oxygen molecule is reduced to
make water molecules. We calculated equilibrium electric potential for
every elementary reaction process, and on that basis, we related
condition to forward the four-electron-reduction with the adsorption
energies of the oxygen atom and the hydroxide molecule. Second, we
examined a ZrO2 electrode to investigate how a metal oxide would work
as a platinum substitute material. As we did for the metal electrode,
we analyzed elementary reaction where a oxygen molecule is reduced
into water molecules. As a result, we found clear difference in the
elementary reaction processes between the two substrates: Two OH
adsorbates are reduced to form HOOH's on the oxide electrode, whereas
the OH adsorbates are dismantled into O and OH after OOH is generated
on the metal electrode. In the case of metal oxide, OH is adsorbed on
the surface exhaustively OH-poisoning the electrode, so the reduction
reaction is significantly hampered. We also found that, for the four
electron reduction, a reduction of OH to generate the water molecule
is a rate-determining process.
Oxygen reduction OR catalysts may share a common physical properties
that would enhance the OR-functionality. To clarify that we focused on
platinum oxide, known metal oxide-based platinum substitute materials,
and calculated the band structures and examined how the oxygen atom
affects the band. We also focused on dielectric constant, bandgap, and
the local density of states at the oxygen site above the Fermi level.
As a result, in comparison with the normal metal oxide, we found that
the oxygen orbital component of the conduction band was large in the
platinum oxide and platinum substitute materials. We proposed that the
oxygen reduction-related catalyst could be characterized by the local
electronic structures near the oxygen site and how HOMO/ LUMO is
located relative to the oxygen 2p level. On this criterion we
extracted 4,000 candidate metal oxides using the world's greatest
inorganic compound database ICSD and screened them using as well the
dielectric constants from a band calculation. Thereby we obtained
platinum substitute compound candidates.
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