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.

No abstract

No abstract

Hydrogen production plays a major role in technologies for renewable energy storage. Water and urea electrolysis (WE, UE) are promising processes in this regard. The oxygen evolution reaction (OER) and urea oxidation reaction (UOR), respectively, are limiting the efficiency of the overall process. As catalysts for these reactions, metal-organic frameworks (MOF) have gained increasing attention due to their combinations and co-existence of metal and organic moiety properties. Here, we investigated the catalytic behavior of Ni MOF (1,3,5-Benzenetricarboxylic acid (BTC)) towards OER and UOR in alkaline medium on carbon paper (CP) as a support. The Ni MOF exhibits 346 mV overpotential (h) at a current density of 10 mA cm À2 , 79.03 A g À1 specific-mass activity at 400 mV of h than compared to wet chemically prepared (WCP) NiO and RuO 2 for OER in 1 M KOH. Meanwhile, % 230 mV of h at 10 mA cm À2 current density with appreciable stability for 12 hours for Ni MOF in 30 % KOH was also observed. For UOR in UE, Ni MOF shows an onset potential of 1.34 V vs. RHE and 63.15 mA cm À2 current density at 1.5 V vs RHE in 1 M KOH in the presence of 1 M urea. The observed results of OER and UOR catalytic behavior are better than wet chemically prepared (WCP) NiO and noble benchmark RuO 2 catalyst under identical conditions. The results suggested that the MOF plays a major role in enhancing the catalytic activity by the facile formation of Ni(OH) 2 /NiOOH, stability and electronic properties due to their porous and interconnected structure.