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Cobalt hydroxide Co(OH)2 is considered to be a potential material for electrocatalyst, especially for oxygen evolution reaction (OER), owing to the earth's abundance, environmentally benign nature, and redox-active properties of cobalt. Herein, we report the fabrication of pristine Co(OH)2 and AgNP-integrated Co(OH)2 (Ag–Co(OH)2) by simple wet chemical methods and explore the electrocatalytic OER activity in the alkaline medium. High-resolution transmission electro-microscopic (HR-TEM) analysis revealed featureless nanostructures for Co(OH)2 with coexisting amorphous and crystalline phases, as well as the inclusion of crystalline AgNPs in Ag–Co(OH)2. X-ray photoelectron spectroscopic (XPS) analysis confirmed the inclusion of metallic AgNPs and the presence of Co at a mixed oxidation state. Electrocatalytic OER studies indicated that pristine Co(OH)2 required the overpotential of 299 mV to achieve a geometric current density of 10 mA cm−2. The integration of AgNPs in Co(OH)2 (Ag–Co(OH)2) showed a gradual improvement in the OER activity. The optimized sample, Ag–Co(OH)2-5, required the overpotential of 253 mV to produce 10 mA cm−2 current density. Tafel slope analysis revealed a lower value upon AgNP integration and electrochemical impedance showed lower charge transfer resistance. The lower Tafel value and charge transfer resistance of Ag–Co(OH)2-5 indicated good chemical coupling and faster reaction kinetics at the electrode surface. AgNPs incorporation with Co(OH)2 also showed enhanced turn-over frequency, electrochemical active surface area, and double-layer capacitance. The fabricated hybrid Ag–Co(OH)2-5 catalyst also exhibited good stability over 60 h. Thus, the electrocatalytic activity of low-cost Co(OH)2 was improved by fabricating coexisting amorphous and crystalline phases and integrating noble silver nanoparticles. [ABSTRACT FROM AUTHOR]

Metal organic framework (MOF) based electrocatalysts have received increased attention in recent years because of their tailorable structure, functionality and porosity. Herein, cobalt-terephthalic acid (CoTPA) based microcrystalline MOFs particles are synthesized in the presence of four different organic amines (DABCO (D), butylamine (B), hexylamine (H) and triethylamine (T)) and the electrocatalytic oxygen evolution reaction was explored. Powder X-ray diffraction (PXRD) analysis confirmed the formation of crystalline CoTPA MOFs with a similar structure but with different faceted orientation. Further, morphological studies revealed the formation of CoTPA MOFs microparticles with different morphologies depending on the amine utilized in the reaction. BET analysis confirmed the porosity with a different surface area and pore diameter. Thermogravimetric analysis indicated the water coordination in all four MOFs. X-ray photoelectron spectroscopy (XPS) analysis indicated the coexistence of Co2+ and Co3+ in the MOFs. All four MOFs exhibited strong OER activity in alkaline medium. CoTPA-D exhibited relatively higher activity and required an overpotential of 273 mV to produce the benchmark current density of 10 mA cm−2 compared to CoTPA-B (281 mV), CoTPA-H (287 mV) and CoTPA-T (278 mV). The low Tafel slope and charge transfer resistance indicated the faster reaction kinetics whereas the higher electrochemical surface area and double layer capacitance (Cdl) suggested the availability of more active sites in CoTPA-D MOFs. The post catalytic analysis suggested the conversion of CoMOFs into CoOOH during electrocatalysis, which resulted in the enhanced OER reaction. Thus, the present work reports the facile preparation of CoMOFs with varied porosity and functionality that resulted in different electrocatalytic OER activity. [ABSTRACT FROM AUTHOR]