To elucidate the mechanism of catalytic activity of metal surfaces on the reaction of hypophosphite ions, which act as a reducing agent for electroless deposition, molecular orbital interactions between hypophosphite ions and metal surfaces were analyzed using density functional theory. Pd (111) and Cu (111) were chosen as the surfaces with high and low catalytic activity, respectively. The electronic states of adsorption systems were analyzed using the Mülliken population analysis. The position of the d-band plays a key role in determining the catalytic activity on P-H bond cleavage of hypophosphite. The Pd surface has a d-band near the Fermi level and contains a vacancy; this enables the donation and back-donation effect to occur on the adsorbed hypophosphite and promotes P-H bond cleavage. On the other hand, the Cu surface has a d-band in the deep energy area and contains no vacancy; the donation and back-donation effect is not induced and P-H bond cleavage is not promoted. This difference in the degree of promotion of P-H cleavage is responsible for the difference in the catalytic activity on P-H cleavage and dehydrogenation of hypophosphite ions, which in turn explains the difference in the catalytic activity during the entire hypophosphite oxidation process.
The electrocatalytic activities of a wide range of intermetallic bulk compounds in the ethanol (EtOH) and methanol (MeOH) oxidation reactions in alkaline media have been studied, and the results have been compared to those of pure polycrystalline Pt and Pd electrodes. The PtPb, PtBi, and PtBi2 intermetallic compounds appeared to be the most promising electrocatalysts among all of the examined bulk electrodes. The current densities at −0.2 V (vs. Ag/AgCl KCl satd.) for PtPb, PtBi, and PtBi2 in EtOH were 21.4, 7.73, and 6.03 mA cm−2, respectively. All of the other intermetallic bulk electrodes exhibited current densities less than 2.5 mA cm−2. PtPb had the lowest onset potential of −0.58 V for EtOH oxidation, which was 20–30 mV less than that of pure Pt and Pd. The current densities of PtPb were at least seventeen times larger than those of pure Pt and Pd. PtBi and PtBi2, which have onset potentials of −0.51 and −0.45 V, respectively, for the EtOH oxidation reaction exhibited extremely stable oxidation currents of 4.8 and 3.3 mA cm−2 during the constant-potential electrolysis of EtOH. The same behavior was also observed for the MeOH oxidation with PtPb, PtBi, and PtBi2 intermetallic compounds.
Barium iron oxide containing hexavalent iron (FeVIO42−) was directly synthesized on iron substrates by anodic oxidation using Ba(OH)2 solution. The lithium (de)intercalation properties were investigated using X-ray diffraction, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, and electrochemical charge/discharge measurements. A 45 nm thick BaFeO4 film exhibited a discharge capacity of 300 mAh g−1, which is close to the theoretical value of 313 mAh g−1 calculated from the three electron reaction between iron VI and III states.