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Structure and stability of an iron-based catalyst for the oxygen reduction reaction, prepared by heat treatment of carbon-supported iron(III) tetramethoxyphenylporphyrin chloride (FeTMPP−Cl), were investigated. The oxygen reduction in acid electrolyte was examined with the rotating (ring) disk electrode. The measurements confirmed that H2O2 is generated as a byproduct of the oxygen reduction. The structural elucidation of the catalyst showed that the porphyrin decomposes during heat treatment. Nitrogen atoms of the heat-treated porphyrin become bonded at the edge of graphene layers as pyridine- and pyrrole-type nitrogen. Two Fe3+ components as well as metallic, carbidic and oxidic iron were detected by Mössbauer spectroscopy. An electrochemical longevity test and two degradation experiments with sulfuric acid and H2O2 showed that H2O2 causes the degradation of active sites. A 6-fold coordinated Fe3+ compound seems to be responsible for the catalytic activity. Only 8% of the primary iron content is present in the active iron component.

Contemporary models are shown to significantly underestimate the attainable efficiency of solar energy conversion to water splitting, and experimentally a cell containing illuminated AlGaAs/Si RuO2/Ptblack is demonstrated to evolve H2 and O2 at record solar driven water electrolysis efficiency. Under illumination, bipolar configured Al0.15Ga0.85As (E g = 1.6 eV) and Si (E g = 1.1 eV) semiconductors generate open circuit and maximum power photopotentials of 1.30 and 1.57 V, well suited to the water electrolysis thermodynamic potential:  H2O → H2 + 1/2O2; E°H 2 O = E O 2 − E H 2 ; E°H 2 O(25 °C) = 1.229 V. The E°H 2 O/photopotential matched semiconductors are combined with effective water electrolysis O2 or H2 electrocatalysts, RuO2 or Ptblack. The resultant solar photoelectrolysis cell drives sustained water splitting at 18.3% conversion efficiencies. Alternate dual band gap systems are calculated to be capable of attaining over 30% solar photoelectrolysis conversion efficiency.

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