Fabrication of a Sealed Electrochemical Microcell for in Situ Soft X-ray Microspectroscopy and Testing with in Situ Co-Polypyrrole Composite Electrodeposition for Pt-Free Oxygen Electrocatalysis

Abstract

In this paper we report on the fabrication and testing of a novel concept of sealed electrochemical microcell for in situ soft X-ray microspectroscopy in transmission, dedicated for nonvacuum compatible electrolytes. The microcell, fabricated using ultraviolet lithography, at variance with previous versions of electrochemical wet cells, that featured an optical window glued on top of the electrode system and a very limited electrolyte volume, the device presented here is a single solid block based around a microfabricated channel with fixed optical windows and apt for microfluidic work. Moreover, this cell allows to employ an advanced electrodic geometry developed in our group - so far used only in open electrochemical cells for work with vacuum-compatible electrolytes - also with low-vapor pressure liquids, possibly saturated with the required gases. The cell optimal electrode design allows three-electrode electrochemical control typical of traditional electrochemical experiments. The first electrochemical experiments with this new cell explore the electrochemical growth of a Co-polypyrrole, a composite electrocatalyst material with promising performance to replace the expensive Pt catalyst in fuel-cell oxygen electrodes. Morphological and chemical-state distributions of Co codeposited with polypyrrole has been followed as a function of time and position, yielding unprecedented information on the processes relevant to the synthesis of this catalyst.

Coelectrodeposition of Ternary Mn-Oxide/Polypyrrole Composites for ORR Electrocatalysts: A Study Based on Micro-X-ray Absorption Spectroscopy and X-ray Fluorescence Mapping

“…The stabilization of higher-valent Mn by doping with two-valent cations is expected on the basis of [53,54] and results to be more effective in the case of co-doping in ternary systems rather than by simple doping with a single species; moreover, galvanic coupling provided by Cu 0 turns out to be even more effective in stabilizing the 4-valent form [55]. forms, coherently with our results on Co/PPy [15,42] and Mn-Co/PPy [40]. The presence of both valences results from the fact that this element is incorporated into the composite by both electrodeposition and electroprecipitation processes taking place during the cathodic and anodic pulse-plating branches, respectively.…”

“…It is the authors' opinion that it is currently difficult to gain a general understanding and consequently of controlling the characteristics of the composites, especially in terms of composition, chemical state, number, size, and spatial distribution of the electrodeposited metal crystals. We therefore reckon that the systematic use of complementary multitechnique ex situ [41], quasi in situ [15] and in situ [42] microspectroscopic tools is required for next generation studies of these systems.…”

“…ORR in alkaline media is a fundamental cathodic reaction in polymer membrane electrolyte fuel cells and metal-air batteries [43]. Among the different materials proposed, a highly attractive class of electrocatalysts is the non-precious metal/polypyrrole system (e.g., [15,41,42,44,45] and references therein). Polypyrrole is an excellent matrix for ORR catalysts for several reasons: (i) its relatively high nitrogen content, that allows the formation of ORR active Me-N sites within the intact polymer structure; (ii) reasonable environmental stability and relatively good robustness with respect to peroxide attack; (iii) high electrical conductivity [46]; (iv) optimal adhesion of catalyitic oxides [47].…”

High‐lateral resolution X‐ray fluorescence microspectroscopy and dynamic mathematical modelling as tools for the study of electrodeposited electrocatalysts

“…This type of materials is a prospective effective and durable alternative to both the traditional materials, based on Pt, and to innovative ones that exhibit potential environmental problems, owing to the use of Co. [2][3][4][5][6][7] In particular, Mn-based systems are currently the most widely used cathodes in metal/air batteries, owing to their low-cost and high catalytic activity for oxygen electroreduction in alkaline solution, resulting from their capability of decomposing hydrogen peroxide. [8][9][10][11] The use of transitional mixed oxides, such as Mn-Cu oxides, incorporated in PPy matrix has shown excellent electrocatalytic activity and good stability even at low pH, where mixed metal oxide cathodes usually undergo degradation.…”

Combining multiple imaging techniques at the TwinMic X-ray microscopy beamline

“…The main constraints are therefore i) suitable thickness to allow some transmission and ii) compatibility with high vacuum (10 -6 mbar). In specific cases, atmospheric or liquid sample environment can be available by encapsulating the specimen inside a specifically designed vacuum-tight container with two Si 3 N 4 membrane windows (14).…”