Tuning the Co Oxidation State in Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ by Flame Spray Synthesis Towards High Oxygen Evolution Reaction Activity

Round 1

Reviewer 1 Report

This paper reports on effect of three synthesis parameters on the properties of perovskite-type oxide Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) for oxygen evolution reaction (OER). The BSCF was synthesized by flame spray synthesis (FSS) technique with different total metal concentrations (CTM), flow rates of the precursor solution (FRPS) and of the dispersion gas (FRDG). This work demonstrates that a lower CTM, a higher FRPS and a lower FRDG produces BSCF with a higher OER activity, leading to change of Co and Fe in a lower oxidation state. This manuscript is well organized with proper experimental evidences such as XAS, XRD and TEM. Thus I recommend its acceptance after some minor modifications. The comments are listed below;

1. The authors concludes that a higher oxygen vacancy concentration of Co and Fe species is crucial for high OER activity. The authors need to explain more detail about how Co and Fe oxygen vacancies contribute to enhanced OER activity. Do the oxygen vacancy sites still exist after OER reaction? Have the authors analyzed the samples after the reaction?
2. In electrochemical reaction, surface analysis is important to understand the catalytic state and phase on surface active sites. Have the authors checked the surface states with XPS analysis for comparing with XANES analysis?
3. Catalytic stability is very important factor in catalytic reactions. The authors need to present the stability results of prepared samples.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

This paper is well organized and written. It involves some valuable findings regarding the influence of flame spray synthesis (FSS) parameters on the oxygen evolution reaction (OER) activity of Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF). This study reveals that—in comparison to CTM—the FRPS and FRDG have a significant influence on the formation of secondary phases—mostly Ba and Sr based carbonates and nitrates—as well as on the specific surface area (SSABET).

The interesting results and conclusions on the effect of these three synthesis parameters on the properties of BSCF as OER active material can be considered as a step forward for a successful scale-up by maximizing the production rate without losing its electrocatalytic activity

I do recommend publication in the present form

Author Response

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Author Response File: Author Response.pdf