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. 2020 Jun 11;13(11):2662.
doi: 10.3390/ma13112662.

The Influence of the Electrodeposition Parameters on the Properties of Mn-Co-Based Nanofilms as Anode Materials for Alkaline Electrolysers

Karolina Cysewska  1 , Maria Krystyna Rybarczyk  2 , Grzegorz Cempura  3 , Jakub Karczewski  4 , Marcin Łapiński  4 , Piotr Jasinski  1 , Sebastian Molin  1
Affiliations

The Influence of the Electrodeposition Parameters on the Properties of Mn-Co-Based Nanofilms as Anode Materials for Alkaline Electrolysers

Karolina Cysewska et al. Materials (Basel). .

Abstract

In this work, the influence of the synthesis conditions on the structure, morphology, and electrocatalytic performance for the oxygen evolution reaction (OER) of Mn-Co-based films is studied. For this purpose, Mn-Co nanofilm is electrochemically synthesised in a one-step process on nickel foam in the presence of metal nitrates without any additives. The possible mechanism of the synthesis is proposed. The morphology and structure of the catalysts are studied by various techniques including scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. The analyses show that the as-deposited catalysts consist mainly of oxides/hydroxides and/or (oxy)hydroxides based on Mn2+, Co2+, and Co3+. The alkaline post-treatment of the film results in the formation of Mn-Co (oxy)hydroxides and crystalline Co(OH)2 with a β-phase hexagonal platelet-like shape structure, indicating a layered double hydroxide structure, desirable for the OER. Electrochemical studies show that the catalytic performance of Mn-Co was dependent on the concentration of Mn versus Co in the synthesis solution and on the deposition charge. The optimised Mn-Co/Ni foam is characterised by a specific surface area of 10.5 m2·g-1, a pore volume of 0.0042 cm3·g-1, and high electrochemical stability with an overpotential deviation around 330-340 mV at 10 mA·cm-2geo for 70 h.

Keywords: alkaline electrolyser; electrocatalyst; electrodeposition; energy material; nanofilm; nickel foam; oxygen evolution reaction.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
(a) Synthesis graphs recorded during the electrochemical synthesis of Mn/Co oxide/hydroxides at −1.1 V vs. Ag/AgCl in an aqueous solution of differently concentrated Mn(NO3)2·4H2O and Co(NO3)2·6H2O with the deposition time limited by a charge of 200 mC; (b–d) SEM images of Mn-Co film deposited on nickel foam in a solution of Mn/Co (2 mM/8 mM) for 200 mC with different magnifications (b,c—surfaces, d—polished cross-section).
Figure 2
Figure 2
(a) XRD patterns of Mn-Co deposited on nickel before (red, triangle), and after (black, cross) alkaline treatment. The most intense diffraction peaks are assigned to Ni foil. XPS scans of (b) Co and (c) Mn of as-deposited and after-alkaline-treatment Mn-Co film. For XRD and XPS, the film was synthesised in a solution of Mn/Co 2 mM/8 mM for 200 mC on nickel foam/foil.
Figure 3
Figure 3
(a) Bright Field (BF) TEM image, and (b) corresponding experimental Selected Area Diffraction (SAED) pattern of Mn-Co film before alkaline treatment; (c) BF-TEM image, area of SAED pattern is marked with red circle, and (d) corresponding experimental SAED pattern from the area, marked on a BF-TEM image with a red circle, of Mn-Co film after alkaline treatment; (e) Experimental SAED pattern of area marked with a red circle, superimposed with simulated, theoretical diffractogram from cobalt manganese (IV/VI) oxide (0.25/1.75/4), (259073-ICSD) Zone Axis [111]; (f–i) TEM elemental mapping images of (g) cobalt, (h) manganese, and (i) oxygen of the Mn-Co film. Mn-Co film for TEM analysis was synthesised in an aqueous solution of Mn/Co 2 mM/8 mM (200 mC).
Figure 4
Figure 4
Evolution of (a) Brunauer–Emmett–Teller (BET) specific surface area, (b) pore volume, and (c) contact angle with an example of an optical microscopy image taken during the measurement of Mn/Co 2 mM/8 mM for bare nickel foam and nickel foam coated with Mn-Co film synthesised under different conditions as a function of the deposition charge.
Figure 5
Figure 5
Linear sweep voltammetry profiles and corresponding Tafel plots for Mn-Co film synthesised in the presence of (a,b) Mn/Co 2 mM/4 mM, (c,d) 2 mM/6 mM, and (e,f) 2 mM/8 mM on nickel foam measured in Ar-purged 1 M KOH.
Figure 6
Figure 6
Evolution of the (a) onset potential, (b) overpotential determined at 10 mA·cm−2, (c) double-layer capacitance, (d) electroactive surface area (ECSA), (e) electrochemical impedance spectra (EIS) measured at 0.7 V vs. Ag/AgCl, and (f) Rct of the oxygen evolution reaction (OER) as a function of the deposition charge for the Mn-Co film synthesised under different conditions on nickel foam.
Figure 7
Figure 7
Chronopotentiometric curve recorded during the stability test of the Mn-Co film on nickel foam synthesised in a solution of Mn/Co 2 mM/8 mM for 200 mC measured in Ar-purged 1 M KOH.
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