An iron-phthalocyanine complex was utilized as a cathode for constructing a one-compartment hydrogen peroxide fuel cell operated under acidic conditions for the first time. The protonation to the phthalocyanine ligand is crucial to exhibit high activity toward hydrogen peroxide reduction. NafionÒ coating of the anode improved the stability of the fuel cell.A new energy carrier instead of fossil fuels should be developed to realize a sustainable development. [1][2][3][4] Hydrogen peroxide (H 2 O 2 ) is a potential candidate as a new energy carrier, because it can be produced by the two-electron reduction of oxygen, which is abundant in air, and also by the two-electron oxidation of water that is more abundant on the earth. [5][6][7] In addition, H 2 O 2 has high energy density with none of the environmental problems caused by most other fuels, because H 2 O 2 decomposes to water and oxygen. [5][6][7] In order to use H 2 O 2 as a green energy carrier, two technological issues should be addressed: one is production of H 2 O 2 by utilizing natural energies such as solar, wind, etc.; the other is production of electricity using H 2 O 2 fuel cells. [7][8][9] We have reported that H 2 O 2 can be produced by using electrical power of a photovoltaic solar cell in the presence of Co porphyrins as catalysts under acidic conditions, when the current efficiency reached nearly 100%. 7 H 2 O 2 thus produced can be used in

The design of molecular electrocatalysts for hydrogen evolution has been targeted as a strategy for the conversion of solar energy to chemical fuels. In cobalt hangman porphyrins, a carboxylic acid group on a xanthene backbone is positioned over a metalloporphyrin to serve as a proton relay. A key proton-coupled electron transfer (PCET) step along the hydrogen evolution pathway occurs via a sequential ET-PT mechanism in which electron transfer (ET) is followed by proton transfer (PT). Herein theoretical calculations are employed to investigate the mechanistic pathways of these hangman metalloporphyrins. The calculations confirm the ET-PT mechanism by illustrating that the calculated reduction potentials for this mechanism are consistent with experimental data. Under strong-acid conditions, the calculations indicate that this catalyst evolves H2 by protonation of a formally Co­(II) hydride intermediate, as suggested by previous experiments. Under weak-acid conditions, however, the calculations reveal a mechanism that proceeds via a phlorin intermediate, in which the meso carbon of the porphyrin is protonated. In the first electrochemical reduction, the neutral Co­(II) species is reduced to a monoanionic singlet Co­(I) species. Subsequent reduction leads to a dianionic doublet, formally a Co(0) complex in which substantial mixing of Co and porphyrin orbitals indicates ligand redox noninnocence. The partial reduction of the ligand disrupts the aromaticity in the porphyrin ring. As a result of this ligand dearomatization, protonation of the dianionic species is significantly more thermodynamically favorable at the meso carbon than at the metal center, and the ET-PT mechanism leads to a dianionic phlorin species. According to the proposed mechanism, the carboxylate group of this dianionic phlorin species is reprotonated, the species is reduced again, and H2 is evolved from the protonated carboxylate and the protonated carbon. This proposed mechanism is a guidepost for future experimental studies of proton relays involving noninnocent ligand platforms.

A stable monoprotonated porphyrin (porphyrin monoacid) was obtained by reaction of saddle-distorted dodecaphenylporphyrin with anthracene sulfonic acids and the crystal structures of the supramolecular assemblies were determined.

A simple but elegant way to obtain linked donor-acceptor entities involving metallomacrocycle complexes with fixed distance and orientation is the use of coordination of axial ligands to metallomacrocycle complexes. A series of electron acceptor-bearing silicon phthalocyanine (SiPc) triads have been readily synthesized, using the six-coordinated nature of the central silicon atom, by attachment of two electron-acceptor units, fullerene SiPc-(C(60))(2), trinitrofluorenone SiPc-(TNF)(2) and trinitrodicyanomethylenefluorene SiPc-(TNDCF)(2). The nitrogen of pyridylnaphthalenediimide (PyNIm) can coordinate to the metal center of zinc porphyrin to form a donor-acceptor complexes: ZnTPP-PyNIm. The binding of pyridine moieties to Zn-porphyrin complexes is much enhanced by the distortion of porphyrin ring. By taking advantage of saddle distortion of zinc octaphenylphthalocyanine (ZnOPPc) and diprotonated dodecaphenylporphyrin (H(4)DPP(2+)), a discrete supramolecular assembly composed of Zn(OPPc) and H(4)DPP(2+) and is obtained by using 4-pyridinecarboxylate (4-PyCOO(-)) with the axial coordination bond and hydrogen bonding. The charge separation in these metal macrocycles linked with electron acceptors with axial coordination bonds is described together with the application to develop supramolecular solar cells.