Electrochemical Performance of Iron-Doped Cobalt Oxide Hierarchical Nanostructure

Role of Fe decoration on the oxygen evolving state of Co3O4 nanocatalysts

The production of green hydrogen through alkaline water electrolysis is the key technology for the future carbon-neutral industry. Nanocrystalline Co3O4 catalysts are highly promising electrocatalysts for the oxygen evolution reaction and their activity strongly benefits from Fe surface decoration. However, limited knowledge of decisive catalyst motifs at the atomic level during oxygen evolution prevents their knowledge-driven optimization. Here, we employ a variety of operando spectroscopic methods to unveil how Fe decoration increases the catalytic activity of Co3O4 nanocatalysts as well as steer the (near-surface) active state formation. Our study shows a link of the termination-dependent Fe decoration to the activity enhancement and a significantly stronger Co3O4 near-surface (structural) adaptation under the reaction conditions. The near-surface Fe- and Co-O species accumulate an oxidative charge and undergo a reversible bond contraction during the catalytic process. Moreover, our work demonstrates the importance of low coordination surface sites on the Co3O4 host to ensure an efficient Fe-induced activity enhancement, providing another puzzle piece to facilitate optimized catalyst design.

Photocatalytic Performance of Organically Templated Cr-Doped Co3O4 in Remediation of Industrial Wastewater: Effect of Order–Disorder in the Lattice

In photocatalysis, the optical properties and surface parameters significantly affect the catalytic performance. To engineer the optical properties and textural structure, Cr and p-phenylene diamine (PDA) were utilized as dopant and textural structure regulator, respectively. A series of Cr-doped Co3O4 with dopant percentages of 0, 1, 3, and 5, templated PDA at a fixed ratio of 5%, and another un-templated sample with a dopant ratio of 5% were prepared. The co-precipitation method was applied in swift and innovative procedures, where a calculated amount of NaOH was used as a precipitant. The optical properties, dopant concentration quenching, and surface parameters are strongly affected by the order–disorder in the lattice and dopant concentration. The lattice regularity affects the optical properties and the surface parameters along with the dopant concentration. The photocatalysts were evaluated in the disposal of organic pollutants in a representative sample of wastewater collected from different industrial activities. The function of another function was applied to monitor the pollutants' disposal, taking the total organic carbon (TOC) as a function of the pollutants' concentration and the photometric absorbance as a function of the TOC. The kinetic investigation exhibited the significant role of the pore system on the reaction rate.

Efficient Recovery Annealing of the Pseudocapacitive Electrode with a High Loading of Cobalt Oxide Nanoparticles for Hybrid Supercapacitor Applications

Electrochemical pseudocapacitors, along with batteries, are the essential components of today's highly efficient energy storage systems. Cobalt oxide is widely developing for hybrid supercapacitor pseudocapacitance electrode applications due to its wide range of redox reactions, high theoretical capacitance, low cost, and presence of electrical conductivity. In this work, a recovery annealing approach is proposed to modify the electrochemical properties of Co₃O₄ pseudocapacitive electrodes. Cyclic voltammetry measurements indicate a predominance of surface-controlled redox reactions as a result of recovery annealing. X-ray diffraction, Raman spectra, and XPES results showed that due to the small size of cobalt oxide particles, low-temperature recovery causes the transformation of the Co₃O₄ nanocrystalline phase into the CoO phase. For the same reason, a rapid reverse transformation of CoO into Co₃O₄ occurs during in situ oxidation. This recrystallization enhances the electrochemical activity of the surface of nanoparticles, where a high concentration of oxygen vacancies is observed in the resulting Co₃O₄ phase. Thus, a simple method of modifying nanocrystalline Co₃O₄ electrodes provides much-improved pseudocapacitance characteristics.