One Electron-Initiated Two-Electron Oxidation of Water by Aluminum Porphyrins with Earth's Most Abundant Metal.
We report herein a new molecular catalyst for efficient water splitting, aluminum porphyrins (tetra-methylpyridiniumylporphyrinatealuminum: AlTMPyP), containing earth's most abundant metal as the central ion. One-electron oxidation of the aluminum porphyrin initiates the two-electron oxidation of water to form hydrogen peroxide as the primary reaction product with the lowest known overpotential (97 mV). The aluminum-peroxo complex was detected by a cold-spray ionization mass-spectrometry in high-resolution MS (HRMS) mode and the structure of the intermediate species was further confirmed using laser Raman spectroscopy, indicating the hydroperoxy complex of AlTMPyP to be the key intermediate in the reaction. The two-electron oxidation of water to form hydrogen peroxide was essentially quantitative, with a Faradaic efficiency of 99 %. The catalytic reaction was found to be highly efficient, with a turnover frequency up to ∼2×104s-1. A reaction mechanism is proposed involving oxygen-oxygen bond formation by the attack of a hydroxide ion on the oxyl-radical-like axial ligand oxygen atom in the one-electron-oxidized form of AlTMPyP(O-)2, followed by a second electron transfer to the electrode.
Department of Applied Chemistry, Center for Artificial Photosynthesis, Tokyo Metropolitan University, 1-1 Minami-ohsawa, Hachiohji, Tokyo, 192-0397, Japan.
Fazalurahman
0000-0003-1607-7814
F
Kuttassery
Department of Applied Chemistry, Center for Artificial Photosynthesis, Tokyo Metropolitan University, 1-1 Minami-ohsawa, Hachiohji, Tokyo, 192-0397, Japan.
Siby
S
Mathew
Department of Applied Chemistry, Center for Artificial Photosynthesis, Tokyo Metropolitan University, 1-1 Minami-ohsawa, Hachiohji, Tokyo, 192-0397, Japan.
Shogo
S
Sagawa
Department of Applied Chemistry, Center for Artificial Photosynthesis, Tokyo Metropolitan University, 1-1 Minami-ohsawa, Hachiohji, Tokyo, 192-0397, Japan.
Sebastian Nybin
SN
Remello
Department of Applied Chemistry, Center for Artificial Photosynthesis, Tokyo Metropolitan University, 1-1 Minami-ohsawa, Hachiohji, Tokyo, 192-0397, Japan.
Arun
A
Thomas
Department of Applied Chemistry, Center for Artificial Photosynthesis, Tokyo Metropolitan University, 1-1 Minami-ohsawa, Hachiohji, Tokyo, 192-0397, Japan.
Daisuke
D
Yamamoto
Department of Applied Chemistry, Center for Artificial Photosynthesis, Tokyo Metropolitan University, 1-1 Minami-ohsawa, Hachiohji, Tokyo, 192-0397, Japan.
Satomi
S
Onuki
Department of Applied Chemistry, Center for Artificial Photosynthesis, Tokyo Metropolitan University, 1-1 Minami-ohsawa, Hachiohji, Tokyo, 192-0397, Japan.
Yu
Y
Nabetani
Department of Applied Chemistry, Center for Artificial Photosynthesis, Tokyo Metropolitan University, 1-1 Minami-ohsawa, Hachiohji, Tokyo, 192-0397, Japan.
Hiroshi
H
Tachibana
Department of Applied Chemistry, Center for Artificial Photosynthesis, Tokyo Metropolitan University, 1-1 Minami-ohsawa, Hachiohji, Tokyo, 192-0397, Japan.
Haruo
0000-0002-8556-1389
H
Inoue
D000535:Aluminum / Q000737:chemistry*; D002384:Catalysis; D004583:Electrons; D006861:Hydrogen Peroxide / Q000138:chemical synthesis* / Q000737:chemistry; D015394:Molecular Structure; D010084:Oxidation-Reduction; D011166:Porphyrins / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization; D013059:Spectrum Analysis, Raman; D014867:Water / Q000737:chemistry*
D011166:Porphyrins; D014867:Water; D006861:Hydrogen Peroxide; D000535:Aluminum
aluminum porphyrins; artificial photosynthesis; hydrogen peroxide; molecular catalysts; water splitting