Bio-inspired nano-composites with polymer matrix as efficient anode materials for electrocatalytic water oxidation – OERNanoCat
The water oxidation into oxygen (OER) remains a bottleneck in the scale-up of water-splitting and CO2-reduction electrolyzers due to slow kinetics and large overpotentials. Key challenges are the development of efficient, robust and cheap earth-abundant OER catalysts and their nanostructuration to improve their efficiency by increasing the active area/volume ratio while reducing the manufacturing cost. OERNanoCat proposes a unique, simple and versatile electrochemical approach to design innovative nanocomposite electrode materials inspired by Photosystem II (PSII), active and stable for water oxidation. These new materials consist of sub-nanosized earth-abundant metal or mixed metal oxides M(M’y)Ox clusters (M/M’ = Ni, Co, Mn, Fe…; M’ = Ca) dispersed into a carboxylate functionalized polymer matrix, mimicking the carboxylates rich environment of the natural Mn4CaO5 cluster of PSII and its sub-nanosized structure, two essential features for an outstanding catalytic efficiency. The presence of carboxylates within the electropolymerized polymer films with excellent complexation properties, will allow to easily incorporate a large variety of cations (Co2+, Ni2+, Mn2+, Fe2+, Ca2+…) by simple coordination and, more importantly, the simultaneous incorporation of several cations in different ratios giving an easy access to mixed metal oxides such as NiFeyOx or MnCayOx, whose catalytic performances are significantly enhanced compared to simple MOx. Once the metal cations are strongly trapped into the polymer matrix by coordination to carboxylates, the simple electro-oxidation of the carboxylate M2+ complexes into high-valent M3+/4+ in water will result in the formation of active metal oxo-bridged M(M’y)Ox clusters, stabilized by hydroxo/water ligands and well dispersed within the polypyrrole film. This oxidative self-assembly process similar to what occurs in the OEC. Some carboxylates could remain partially coordinated to the M(M’y)Ox clusters, while the others will promote PCET reactions, contributing to improve the OER activity. Electrochemical techniques will allow to determine the performances and the associated mechanism.
The OER performances of these bioinspired materials with a majority of catalytic active species will challenge the existing ones with larger size metal oxide catalysts.
X-ray absorption (XAS) and Infra-red (IR) spectroscopies under in situ and operando conditions will be indispensable tools to probe the formation and activity of the M(M’y)Ox catalysts under catalytic conditions, to determine the size of the clusters formed (EXAFS) and their coordination by carboxylate ligands and to identify the active sites and the role of each metal in bimetallic catalysts by monitoring the oxidation state (XANES) and coordination (EXAFS, IR) under applied potentials. Despite the very small size of the metal oxides, their high concentration within the films will allow signal detection, as demonstrated by preliminary experiments performed at Synchrotron Soleil.
This proposal will give a unique opportunity to evaluate the efficiency of sub-nanosized metal species, at the frontier of molecular and heterogeneous catalysts, in catalysis, and to advance the mechanism understanding of water oxidation by metal oxides. This simple all electrochemical approach to design efficient innovative bioinspired materials for OER is novel and offers infinite possibilities in the composition of the catalyst/matrix system.
The consortium with 2 partners (M.-N. Collomb, DCM-UGA Grenoble and B. Lassalle (Synchrotron Soleil, Paris), offers optimal competences, complementarities and synergies. P1 will be in charge of the elaboration and basic characterisations of the nanocomposites, electrocatalysis for OER and electrochemical mechanistic analysis and P2, of the XAS an IR studies and analysis.
Madame Marie-Noëlle Collomb (DEPARTEMENT DE CHIMIE MOLECULAIRE)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
SOLEIL Synchrotron SOLEIL
DCM DEPARTEMENT DE CHIMIE MOLECULAIRE
Help of the ANR 400,616 euros
Beginning and duration of the scientific project: September 2022 - 54 Months