Interplay between synthesis conditions, crystal structure, morphology and OER activity of AgFeO2 delafossite materials

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In this current study, delafossite type AgFeO2 materials were synthesized using the hydrothermal method. Depending on synthesis temperature (115, 155 or 180 oC) and NaOH mineralizer mass (1.0, 1.6, 2.0 or 2.4 g) amount, the delafossites were composed of either mixed-phase 3R/2H-AgFeO2 or single-phase 3R-AgFeO2 crystals. Higher temperatures and NaOH mass were helpful to the growth of µm-sized 3R (space group of R-3m) crystals while lower temperatures and mineralizer mass produced nm-sized 2H (space group of P63/mmc) crystals. The comparison of different delafossite samples revealed that the oxygen evolution reaction (OER) current was larger in mixed-phase materials. Also, the transition from two-phase system to single-phase system was accompanied with a sudden drop in OER current. On the other hand, the difference between the electrochemical behavior of 3R and 2H phase delafossite is discussed in detail by considering similar studies in the literature.