Catalysis of the Water Oxidation Reaction in the Presence of Iron and a Copper Foil.

The oxygen evolution reaction (OER) can provide electrons for reducing water, carbon dioxide, and ammonia. On the other hand, copper compounds are among the most interesting OER catalysts. In this study, water oxidation of a Cu foil in the presence of K2FeO4, a soluble Fe source, under alkaline conditions (pH ≈ 13) is investigated using electrochemical methods, X-ray diffraction, X-ray photoelectron spectroscopy, in situ visible spectroelectrochemistry, Raman spectroscopy, and scanning electron microscopy. After the reaction of the Fe salt with the Cu foil, a remarkable improvement for OER is recorded, which indicates that either the Fe ions on the copper foil directly participate in OER or these ions are critical for activating copper ions on the surface toward OER. Indeed, a remarkable decrease (130 mV) in the overpotential is recorded for the Cu foil in the presence of [FeO4]2-. Tafel slopes for the Cu foil in the absence and presence of K2FeO4 are 113.2 and 46.4 mV/decade, respectively. X-ray photoelectron spectroscopy shows that there is a strong interaction between Cu(II) and Fe(III) on the surface of the Cu foil. During OER in the presence of Cu(II) (hydr)oxide, Cu(III) is detected. In situ visible spectroelectrochemistry shows that Cu and Fe ions are dynamically active and precipitate on the surface of the counter electrode during cyclic voltammetry (CV). The isotopic experimental data using H218O based on Raman spectroscopy show that there is no change in the lattice oxygen. All of these experiments adopt a new perspective on the role of Fe in OER in the presence of a Cu foil under alkaline conditions.

Finding the True Catalyst for Water Oxidation at Low Overpotential in the Presence of a Metal Complex.

The design of molecular-based catalysts for oxygen-evolution reaction (OER) requires more investigations for the true catalyst to be found. First-row transition metal complexes are extensively investigated for OER, but the role of these metal complexes as a true catalyst is doubtful. Some doubts have been expressed about the role of first-row transition metal complexes for OER at high overpotentials (η > 450). Generally, the detection of the true catalyst has so far been focused on high overpotentials (η > 450) because at low overpotentials (η < 450), many methods are not sensitive enough to detect small amounts of heterogeneous catalysts on the electrode surface during the first seconds of the reaction. Ni(II) phthalocyanine-tetra sulfonate tetrasodium (1) is in moderate conditions (at 20-50 °C and pH 5-13) in the absence of electrochemical driving forces, which could make it noteworthy for OER. Herein, the results of OER in the presence of 1 at low overpotentials under alkaline conditions are presented. In addition, in the presence of Ni complexes, using an Fe ion is introduced as a new method for detecting Ni (hydr)oxide under OER. Our experiments indicate that in the presence of a homogeneous OER (pre)catalyst, a deep investigation is necessary to rule out the heterogeneous catalysts formed. Our approach is a roadmap in the field of catalysis to understand the OER mechanism in the presence of a molecular Ni-based catalyst design. Our results shown in this study are likely to open up new perspectives and discussion on many molecular catalysts in a considerable part of the chemistry community.