Catalysts for the oxygen evolution reaction (OER) play an important role in the conversion of solar energy to fuel of earth-abundant water into H and O through splitting/electrolysis. Heterogeneous electrocatalysts for hydrogen and oxygen evolution reactions (HER and OER) exhibit catalytic activity that depends on the electronic properties, oxidation states, and local surface structure. Spinel ferrites (MFeO; M = Ni and Co) based materials have been attractive for the catalytic water oxidation due to their well-known stability in alkaline medium, easy synthesis, existence of metal cations with various oxidation states, low cost, and tunable properties by the desired metal substitution. To understand the better catalytic activity of MFeO in detail the role of Ni and Co was studied through MNiFeO (M = Co; 0 < x < 1), which was prepared by the sol-gel method. The results showed that bare NiFeO has better catalytic activity (η = 381 mV at 10 mA cm and Tafel slope of 46.4 mV dec) compared to Co-containing MNiFeO (η = 450-470 mV at 10 mA cm and Tafel slope of 50-73 mV dec) in alkaline medium, and the substitution of Co is found to suppress the catalytic activity of NiFeO. The degradation of catalytic activity with an increase in Co content was accounted for in further detailed investigations.

Atomic layer fabrication of biphasic spinel Co3O4 and CoO on an FTO substrate through pulsed laser deposition was achieved and the fabricated CoxOy interface was found to undergo tremendous surface construction under an applied potential which eventually increased the activity by reducing the overpotential by 55 mV.

Molybdenum trioxide (MoO) is a well-known electrochromic material. In the present work, n-type α-MoO thin films with both direct and indirect band gaps were fabricated by varying the laser repetition (ablation) rate in a pulsed laser deposition (PLD) system at a constant reactive O pressure. The electrochromic properties of the films are compared and correlated to the microstructure and molecular-level coordination. Mixed amorphous and textured crystallites evolve at the microstructural level. At the molecular level, using NMR and EPR, we show that the change in the repetition rate results in a variation of the molybdenum coordination with oxygen: at low repetition rates (2 Hz), the larger the octahedral coordination, and greater the texture, whereas at 10 Hz, tetrahedral coordination is significant. The anion vacancies also introduce a large density of defect states into the band gap, as evidenced by XPS studies of the valence band and supported by DFT calculations. The electrochromic contrast improved remarkably by almost 100% at higher repetition rates whereas the switching speed decreased by almost 6-fold. Although the electrochromic contrast and coloration efficiency were better at higher repetition rates, the switching speed, reversibility, and stability were better at low repetition rates. This difference in the electrochromic properties of the two MoO films is attributed to the variation in the defect and molecular coordination states of the Mo cation.