電解質のpHが酸素還元反応に影響する
Jay T Bender1, Rohan Yuri Sanspeur2, Nicolas Bueno Ponce3
1McKetta Department of Chemical Engineering, University of Texas at Austin, Austin, Texas 78712, United States.
Journal of the American Chemical Society
|October 1, 2025
まとめ
電解質のpHは酸素還元反応 (ORR) の速度に大きく影響し,特に金や銀のような弱い結合力を持つ触媒には影響する. これは,中間結合エネルギーを変化させ,触媒の活動に影響を与える電場によるものです.
科学分野:
- 電気化学
- 材料科学
- カタリシス
背景:
- 酸素還元反応 (ORR) の動力学と選択性に影響する重要な要因である.
- 様々な触媒でpHがORR率に影響する正確なメカニズムは不明である.
- これらのpHに依存する効果を理解することは,効率的な電気触媒の設計に不可欠です.
研究 の 目的:
- 異なる金属触媒のORR率のpH感度の変化の根本的な理由を解明する.
- 触媒と電解質の接点における電場がpH効果を媒介する役割を調査する.
- 中間結合エネルギーの変化と観測されたORR速度の変動を相関させる.
主な方法:
- 様々な金属の電極 (Pt, Ir, Ru, Pd, Au, Ag) で ORRの実験的運動研究
- 電場効果と中間結合エネルギーをモデル化するための原子模擬.
- ORRメカニズムにおける陽子結合電子移転 (PCET) と非PCETステップの分析.
主要な成果:
- 強い結合力を持つ金属 (Pt, Ir, Ru, Pd) のORR率は,中間結合エネルギーが電気場によって最小限に影響されるため,弱いpH依存性を示す.
- 弱結合金属 (Au,Ag) のORR率は,負の電場によって吸収されたO2の安定化により,アルカリ性電解質で著しく増加する.
- ORRの速度決定段階はpHによって変化しませんが,O2吸収のための活性化バリアは弱い結合触媒で減少します.
結論:
- ORRに対するpHの影響は,主に,電気場による中間結合エネルギーの変化によって引き起こされる.
- 強く結合する触媒はpH感度が低く,弱い結合する触媒は高い感度を示します.
- 電解質のpHを調整すると,特に弱い結合物質の吸着障壁を修正することによってORR運動を調整できます.
関連する概念動画
Electrolysis
30.2K
In a galvanic cell, the electrical work is done by a redox system on its surroundings as electrons produced by the spontaneous redox reactions are transferred through an external circuit. Alternatively, an external circuit does work on a redox system by imposing a voltage sufficient to drive an otherwise nonspontaneous reaction in a process known as electrolysis. For instance, recharging a battery involves the use of an external power source to drive the spontaneous (discharge) cell reaction in...
30.2K
Redox Equilibria: Overview
1.5K
A reduction-oxidation reaction is commonly called a redox reaction. In a redox reaction, electrons are transferred from one species to another rather than being shared between or among atoms. The reducing agent or reductant is the species that loses electrons and gets oxidized in the process. The species that gains electrons and gets reduced in the process is the oxidizing agent or oxidant. Redox reactions are represented as two separate equations called half-reactions, where one equation...
1.5K
Redox Reactions
58.3K
Oxidation-reduction or redox reactions involve the transfer of electrons from one molecule or atom to another. When an atom gains an electron, another atom must lose an electron, meaning oxidation and reduction must occur together. Since the redox occurs in pairs, the atom that gets oxidized is also called the reducing agent or reductant, and the atom that is reduced is also called the oxidizing agent or oxidant. A straightforward way to remember the definitions of oxidation and reduction is...
58.3K
Redox Reactions
904
Redox reactions are vital biochemical processes that underpin energy metabolism in cells. These reactions involve the transfer of electrons between molecules, occurring in tandem as oxidation and reduction. Oxidation refers to the loss of electrons, while reduction denotes their gain. This coupling ensures the seamless flow of electrons through metabolic pathways. For example, in bacterial metabolism, glucose undergoes oxidation to carbon dioxide, while oxygen is simultaneously reduced to...
904
Oxidation-Reduction Reactions
75.0K
Oxidation–Reduction Reactions
75.0K
Ladder Diagrams: Redox Equilibria
768
Ladder diagrams are useful tools for understanding redox equilibrium reactions, especially the effects of concentration changes on the electrochemical potential of the reaction. The vertical axis in the redox ladder diagrams represents the electrochemical potential, E. The area of predominance is demarcated using the Nernst equation.
Consider the Fe3+/Fe2+ half-reaction, which has a standard-state potential of +0.771 V. At potentials more positive than +0.771 V, Fe3+ predominates, whereas Fe2+...
Consider the Fe3+/Fe2+ half-reaction, which has a standard-state potential of +0.771 V. At potentials more positive than +0.771 V, Fe3+ predominates, whereas Fe2+...
768


