Protolytic behavior of water-soluble zinc(II) porphyrin and the electrocatalytic two-electron water oxidation to form hydrogen peroxide

Effective Hydrogen Peroxide Production from Electrochemical Water Oxidation

“…Since 2004, a plethora of materials have been investigated for their capability to catalyze the 2 e – WOR, including metal oxides (MnO x , BiVO 4 , CaSnO 3 , ZnO, C,N-TiO 2 , Bi 2 WO 6 :5%Mo, InSbO x , Sb 2 O 3 ), − molecular metal porphyrins (AlTMPyP, SiTPyP, ZnTMPyP, SnTMPyP), − metal-free polymers, and carbon fibers. , The proposed catalysts achieve distinct results concerning the faradaic efficiency (%FE) of the reaction and the production rate of H 2 O 2 , yet all possess one common trait, namely their inability to operate at the high current densities (>100 mA cm –2 ) required for the large-scale implementation of the 2 e – WOR. An initial study by this group on boron-doped diamond (BDD) achieved a maximal H 2 O 2 production rate of 19.7 μmol cm –2 min –1 at 295 mA cm –2 , albeit at the cost of a lower %FE (28%), showcasing BDD as a prospective catalyst candidate for the 2 e – WOR to electro-synthesize H 2 O 2 .…”

Understanding the factors governing the water oxidation reaction pathway of mononuclear and binuclear cobalt phthalocyanine catalysts

“…[7][8][9][10][11][12] Taking advantage of the well-dened coordination structure, homogeneous metal complexes have been developed as typical OER catalysts and models for understanding the fundamental reaction pathways of water oxidation. [13][14][15][16][17][18][19] For example, a copper bipyridine complex was reported for water oxidation, and Cu(III)-OH intermediate species was determined to be responsible for O-O bond formation via a water nucleophilic attack mechanism. 20,21 Besides, metal complexes with macrocyclic ligands, such as porphyrin and corrole ligands, 17,22,23 were also investigated as OER catalysts owing to their robust coordination environment during the oxidation process, in which O-O bond formation proceeds mostly through a macrocyclic radical cation intermediate species and the macrocyclic ligand could serve as an oxidation charge reservoir for the OER.…”

Recent Advances in Electrochemical Water Oxidation to Produce Hydrogen Peroxide: A Mechanistic Perspective

“…Substituting Al for Si or Zn in the porphyrin catalyst still produces H 2 O 2 via similar mechanisms. 62,63 It should be noted that the Si analogue [meso-tetrapyridylporphyrinatesilicon(IV), SiTPyP] has a smaller equilibrium constant compared to the Al porphyrin catalyst (1.2 × 10 2 M −1 vs 2.4 × 10 3 M −1 ) allowing it to release H 2 O 2 more readily. However, SiTPyP also achieved a lower overall current density compared to its Al analogue.…”

“…In 2017, Kuttassery et al developed hydrophilic Al porphyrins as molecular catalysts for the 2 e – WOR with a remarkably low overpotential of 97 mV . The same group introduced a series of similar molecular catalysts using Si, Zn, and Sb porphyrins, with the Zn analogue [zinc­(II) 5,10,15,20-tetrakis­( N -methylpyridinium-4′-yl)­porphyrin, ZnTMPyP] recording an overpotential of just 60 mV in an alkaline environment. − Increased efficiencies for H 2 O 2 production were also achieved when the electrolyte included additives like Na 2 CO 3 or Bu 4 NHPO 4 …”