Cathodic Synthesis of Birnessite Films for Pseudocapacitor Application

Abstract

Cathodic reduction of an aqueous solution of potassium permanganate in the presence of various alkaline metals except for Na + ions led to a deposition of birnessite-type layered MnO 2 . The highest crystallinity was achieved in a bath containing 2 mM KMnO 4 and 50 mM KCl by applying a constant potential of 0 V vs Ag/AgCl. The cathodic formation of birnessite was prevented by the presence of divalent cations, and Na + ions yielded an amorphous or low crystalline product. The birnessite film thus formed showed excellent pseudocapacitive characteristics in its asdeposited state; i.e., a specific capacitance as high as 322 F g -1 at a potential scan rate of 2 mV s -1 , which is much higher than that (75 F g -1 ) of the birnessite film prepared anodically from Mn 2+ ions.

(Invited) Fabrication and Operation under the Same Conditions: Oxygen Reduction on Electrodeposited Manganese Oxide

“…The alternative cathodic deposition from permanganate solutions allows for neutral and alkaline conditions. This less known process recently attracted attention as a tool to fabricate the materials for supercapacitors (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13). The cathodic deposition from neutral permanganate solutions under potentiostatic (2,4,6), galvanostatic (3,5), pulse (9) and voltammetric (10) modes was reported.…”

Electrodeposition: a versatile, efficient, binder-free and room temperature one-step process to produce MnO2 electrochemical capacitor electrodes

“…18-0802) conrming the Na-birnessite structure formation. 12,22 It is important to highlight that the Na-birnessite structure, obtained in this work, is only stabilized by the presence of Na + cations which is present in the electrochemical bath. If no Na 2 SO 4 is initially present, amorphous electrodeposits are achieved as illustrated in Fig.…”

“…By employing permanganate (MnO 4 À )-based bath, birnessite-type MnO 2 electrodes are directly obtained with no further heat treatment. Although, some papers have described the production of MnO 2 EC electrodes by this method, 12,14,17 as far as we know, the inuence of the applied current density on the structure and capacitive performance of MnO 2 electrodes has not yet been described. Here, it is demonstrated by means of X-ray diffractometry (XRD) that a crystalline/amorphous structural transition is observed as the applied current density is increased up to 50 mA cm À2 .…”

Efficient Electrochemical Water Oxidation and Oxidative Degradation of Rhodamine B: A Comparative Study Using High‐Purity Birnessites Containing Li+, Na+ or K+ Ions

“…Some Mn 4+ ions were replaced by Mn 3+ in the synthesis of birnessite, causing triclinic symmetry defect . Due to negative charges generated by Mn 3+ , cations easily intercalated the interlayer into neutralize charges .…”