Intitulé du sujet: Immobilization of thin multifunctional layers onto graphene materials and their use in electrocatalysis

Sujet

Codirection:

Nombre de mois: 48 mois

Ecole Doctorale: ED 388 - Chimie physique et Chimie analytique de Paris centre

Unité de recherche et équipe:

Laboratoire Interfaces Traitements Organisation et DYnamique des Systèmes – ITODYS, UMR- CNRS 7086,  Université Paris Cité

Coordonnées de l’équipe:

ElectroChimie et Surface Active (ECSA) ITODYS UMR-CNRS 7086

Bâtiment Lavoisier - 15, rue Jean-Antoine de Baïf - 75013 PARIS

Secteur: Sciences Physiques et Ingénierie / Physical sciences and Engineering

Langue attendue: Anglais

Niveau de langue attendu: B1

Description

Description du sujet:

 Summary of the thesis:

The thesis proposal addresses the crucial role of surface functionalization and electrocatalysis in advancing energy conversion and storage technologies, particularly for hydrogen and oxygen evolution reactions (HER and OER). The challenge lies in mastering the chemical composition and organization of graphene materials to enhance their properties and reactivity. The project aims to combine surface grafting onto graphene with advanced catalytic materials. The covalent immobilization of functional ionic layers containing heteroatoms (like nitrogen, sulfur, and phosphorus) onto graphene will be performed using diazonium grafting. This approach seeks to develop metal free, more efficient, durable, and sustainable catalysts by controlling the thickness, composition, and structure of the modified graphene. In addition, the generated functional graphene will be used as a support for hosting metal catalyst and thus providing hybrid materials. The project will systematically investigate the relationship between surface structure and catalytic performance. Increasing our understanding of the role of heteroatoms and ionic properties in electrocatalysis aspires to overcome current limitations in water-splitting technologies, providing a more efficient path to clean energy solutions.

Keywords: Surface functionalization, electrochemistry, diazonium chemistry, graphene, electrocatalysis    

Context:

Water splitting, which involves the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), is a promising method for developing new energy technologies that address the fossil fuel crisis and environmental pollution.[1] The development of highly efficient and durable electrocatalysts, coupled with a comprehensive grasp of their intrinsic characteristics, remains significant challenge in the field of electrochemistry. In the fields of materials science and electrochemistry, surface functionalization and electrocatalysis are pivotal concepts driving advancements in energy conversion and storage technologies. This synergy between surface science and electrochemistry offers the potential for significant breakthroughs, addressing both current challenges and future demands.[2] Recently, one promising strategy for enhancing electrocatalyst performance is the use of heteroatom-doped materials. By selecting specific heteroatoms, such as nitrogen, sulfur, or phosphorus, catalytic properties can be fine-tuned for targeted reactions.[3] Nevertheless, the incorporation of dopants into catalysts typically involves a complex, multi-step synthesis process and often necessitating harsh experimental conditions.[4] Furthermore, accurately quantifying the amount of dopants and elucidating their intricate interactions with the catalyst matrix continue to be significant challenges. Yet the challenge lies not just in functionalizing surfaces but also in mastering the factors that influence their organization and chemical composition, which are essential for optimizing their interfacial properties and reactivity. Among surface modification techniques, diazonium electrografting stands out as an effective method for forming covalent bonds between organic layers and electrodes.[5] This technique is renowned for producing highly stable layers and enables the rapid modification of various substrates. Recent advances allow for precise control over layer structure, including adjustable thickness (from monolayers to multilayers), tunable surface concentration, and surface nano-structuring.[6] In comparison to current state-of-the-art, surface modification of nanocarbon materials combined with electrocatalysis is still in its early stages, and several fundamental questions regarding electron transfer properties, surface organization, chemical composition and the contribution of the functional group are not fully committed.

Thesis objectives:

The thesis proposal aims to develop an innovative strategy that combines surface grafting onto graphene with advanced catalytic materials to create more efficient and durable catalysts for HER and OER, thereby advancing clean energy technologies. Despite the growing interest in developing more efficient and stable electrocatalytic systems for energy production, the thesis aims on investigating the relationship between the structure of immobilized organic layers, combining heteroatom’s and ionic properties, onto graphene materials and metal catalysts. This project focuses on establishing structure-property relationships within hybrid graphene based nanomaterials to enhance the HER and OER catalytic processes.

The thesis work plan is divided on three parts to achieve the target objectives.

1. The first part of the thesis will be devoted to generate modified graphene through the covalent grafting of multifunctional layers. For this purpose, the synthesis of novel ionic diazonium derivatives and their immobilization on carbon support will be performed with controlled structure and investigating their electrochemical properties. The strategy involves synthesizing diazonium derivatives bearing either nitrogen heteroatom in the form of imidazolium (positively charged) or negatively charged heteroatoms such as sulfur (S) or phosphorus (P). Different immobilization strategies will be studied including electrochemical and spontaneous grafting. The functional graphene nanomaterials will be characterized using electrochemical and spectroscopic methods to estimate the surface coverage and the doping level. All generated materials will be characterized using various techniques including electrochemistry, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), infrared spectroscopy (IR), and atomic force microscopy (AFM). Key parameters such as electron transfer rate constant, surface coverage, and double layer capacitance will be examined.  

2. The second part of the thesis will focus on generating hybrid nano catalyst materials using the functionalized graphene as host-guesting platform for the electrochemical growth of model catalyst materials. The presence of the attached layers will strongly modify the electrical double layer at the electrode/electrolyte interface and as consequence affect the properties of the deposited metal catalyst. For this purpose, the nature of the deposited materials will be adapted depending on the targeted catalytic reaction HER or OER. To evaluate the impact of ionic layers and heteroatom’s model catalysts (Pd, Ni, and Fe) will be investigated. All the resulting hybrid surfaces will be characterized using electrochemical and spectroscopic methods to achieve several objectives: controlling the shape and size of the NPs, evaluating the electron transfer properties of the graphene after NP introduction, and quantifying the deposited NPs. Finally, localized electrochemical microscopy (SECM) will be employed to investigate the electron transfer dynamics at the nano and micrometric scale over the modified graphene.[7] This will help to evaluate how the ionic properties of the attached layers influence electron transfer behavior at the microscale.

3. The last part of the thesis will concern the investigation of the electrocatalytic performances of the generated graphene materials toward HER and OER. This comprehensive investigation encompasses two distinct categories of catalysts, metal-free catalysts derived from functionalized graphene, as developed in the first part of the thesis, and hybrid graphene materials, which will be engineered in the second part of the research. Understanding of the role of heteroatoms and ionic properties within the same material during electrocatalysis is the main goal of this part. The generated hybrid surfaces are expected to enhance electronic properties, improve charge transfer, and affect surface interactions with reaction intermediates. Overall, by strategically designing and modifying surfaces, the target hybrid materials aim at lowering the overpotential required to drive the HER and OER and increasing the reaction kinetics compared to catalysts supported on unmodified graphene. After thoroughly studying the impact of the structure of these hybrid materials on their properties, we will investigate the electrocatalytic performance of the hybrid functional graphene using various techniques such as linear sweep voltammetry (LSV), impedance spectroscopy, and stability tests. These results will be compared to state-of-the-art catalysts to assess improvements in performance.

Compétences requises:

A Master’s degree (or equivalent) in Chemistry, Materials Science or a closely related discipline.

The PhD candidate should have a strong knowledge in surface science. Background in electrochemistry and electrocatalysis would be an advantage.

Références bibliographiques:

[1]. Shih A. J. Koper M. T. M. et al. Water electrolysis. Nat. Rev. Methods primers. 2022, 2, 84.

[2]. Do V-H. Lee J-M. Surface engineering for stable electrocatalysis. Chem. Soc. Rev. 2024, 53, 2693.

[3]. Liu Z. He T. Jiang Q. Wang W. Tang J. A review of heteroatomic doped two-dimensional materials as electrocatalysts for hydrogen evolution reaction. Int. J. Hydrogen Energy 2022, 47, 29698.

[4]. Nagappan S. et al. Implementation of heteroatom-doped nanomaterial/core–shell nanostructure based electrocatalysts for fuel cells and metal-ion/air/sulfur batteries. Mater. Adv. 2022, 3, 6096-6124.

[5]. Gautier C. López I. Breton T. A post-functionalization toolbox for diazonium (electro)-grafted surfaces: review of the coupling methods. Mater. Adv. 2021, 2, 2773.

[6]. (a) Yu, H.-Z. Ghilane, J. Metal-supported cathodically activated graphite via self-reduction as electrocatalysts for efficient hydrogen evolution reaction Materials Today Chemistry, 2022, 26, 101099. (b) Hapiot P. Lagrost C. Leroux Y.R. Molecular nano-structuration of carbon surfaces through reductive diazonium salts grafting. Curr. Opin. Electrochemistry. 2018, 7, 103.

[7]. (a) Pham-Truong, T.-N. Mebarki, O. Ranjan, C. Randriamahazaka, H. Ghilane, J. Electrochemical Growth of Metallic Nanoparticles onto Immobilized Polymer Brush Ionic Liquid as a Hybrid Electrocatalyst for the Hydrogen Evolution Reaction ACS Appl. Mater. Interf. 2019, 11(41), 38265-38275. (b) Pham-Truong, T.N. Deng, B. Liu, Z. Randriamahazaka, H. Ghilane, J. Local electrochemical reactivity of single layer graphene deposited on flexible and transparent plastic film using scanning electrochemical microscopy Carbon, 2018, 130, 566-573.