SPINEL TYPE ZnCo₂O₄ COATINGS FORMATION AND ELECTROCHEMICAL PERFORMANCE

Photoelectrochemical (PEC) water splitting has been widely considered as one of the most promising technologies in clean, green, and renewable energy production [1]. Moreover, numerous studies suggest that various transition metal oxides are the most promising candidates as photoanodes for PEC materials, especially when used in conjunction.

Our aim was to synthesize p-n heterostructure of spinel type ZnCo₂O₄ coatings, investigate the influence of morphology on its photoelectrochemical properties, and test them as prospective materials to catalyze oxygen evolving reaction (OER).

Spinel type ZnCo₂O₄ coatings were synthesized using two-step process (Fig.1):

chemical precipitation (Zn:Co ratio 1:2 and 1:1) and thermal decomposition at 500 °C for 2 h,

spin-coating technique (the rotation speed of 1000 and 1200 RPM)

Composition, structure and morphology were investigated using various techniques such as: scanning electron microscopy (SEM), adsorption / desorption measurements, X-ray energy dispersion spectroscopy (EDS), X-ray diffraction (XRD), N₂ adsorption / desorption measurements and specific surface area calculations were used. Galvanostatic charge-discharge measurement and linear sweep voltammetry were used in order to investigate photoelectrochemical properties and coatings capacitance.

Ratio change from 1:1 of Zn:Co to 1:2 led to formation of different structure, morphology and properties:

The obtained Zn:Co 1:1 coatings were more rough, granular and thicker (662 nm); with pore size 18.32 nm and 0.55 cm³/g volume, as well as 57.92 m²/g specific surface area and active surface area A=0.14 cm² at E=0.85 V vs. Ag, AgCl|KCl(sat). These coatings demonstrated the incident- to photon efficiency (IPCE) of 22.4% and the applied bias photon-to-current (ABPE) 3.18%;

Zn:Co 1:2 coatings formed uniform, 442 nm thick, vertically, horizontally aligned porous lamellar sturcture; pore size 17.97 nm and 0.14 cm³/g volume, 24.41 m²/g specific surface area; active surface area A=0.26 cm², at E=0.85 V vs. Ag, AgCl|KCl(sat) IPCE 37%; ABPE 5.91%.

Due to great photoelectrochemical performance, we anticipate that the comprehensive analysis of such p-n heterostructure ZnCo₂O₄ will be important for future applications in OER.