IMaFECy · Impact of Magnetic Fields on Electrochemistry - Fundamental Aspects and Fututre Applications

Impact of Magnetic Fields on Electrochemistry - Fundamental Aspects and Fututre Applications

Final Project Report – Marie Curie IEF – Project IMaFECy (No. 327706) Electrochemistry is key for a number of industrial applications, covering both synthetic and analytical aspects. Examples span from the large scale production of aluminium, the electrochemical deposition of homogeneous layers for corrosion protection, across batteries and fuel cells, all the way to electrochemical detection and quantification of heavy metal ions in waste water or glucose levels in human blood. In many cases the inefficient mass transport of species in solution limits electrochemical conversion or sensing applications, thus major efforts have been made in the past to overcome these limitations. Amongst the various approaches of doing so, the application of an external magnetic field is one of the experimentally most simple and convenient, yet also fundamentally least understood options. Notably the successful exploitation of magneto-electrochemistry, has to date been limited to the macro- and micro-scale, while the emerging field of nano-electrochemistry has been widely excluded. The project IMaFECy (Impact of Magnetic Fields on Electrochemistry - Fundamental Aspects and Future Applications) increased the general understanding of magnetic field effects on electrochemical systems and extended the beneficial applications of magnetic fields to the nanoscale. A key aspect of the IMaFECy project was to resolve fundamental scientific controversy in both the fields of magneto- and nano-electrochemistry. This was achieved through a combined experimental and theoretical approach. The main findings of the projects are: i) Single nanoparticle impact experiments (nano-impacts) enabled the first-ever detection of magnetic field-induced agglomeration of solution-phase magnetic nanoparticles alongside with the in-situ sizing of the formed agglomerates (see Fig. 1a). ii) The electrochemical dissolution of individual superparamagnetic magnetite (Fe3O4) nanoparticles was found to be strongly retarded in their magnetized state as compared to their dissolution in their non-magnetic state. Thus, the influence of the magnetic gradient force has been demonstrated on a single nanoparticle for the first time. iii) The magnetic gradients established at superparamagnetic nanoparticles can be used to enhance the mass transport to electrodes modified with such nanoparticles thanks to the local action of the magnetic gradient force. The application and removal of an external magnetic field allows to conveniently and repeatedly switch this effect on and off. iv) Nano-impacts not only allow the characterisation of individual metal nanoparticles (for instance their size and concentration) in simple electrolytes, but their use can be extended to characterise metal oxide, carbonaceous and organic nanoparticles as well as to study metal nanoparticles in complex liquid environments, such as sea water. v) In addition to direct nanoparticle characterisation, nano-impacts can also provide valuable physico-chemical insights not accessible by any other technique. Thus, for instance the electrostatic interactions between nanoparticles and charged surfaces can be measured, the potential of zero charge of graphene nanoplatelets and the agglomeration of silver nanoparticles, can be monitored in solutions of various compositions and ionic strengths. vi) A new electrochemical technique has been developed that enables the characterization of core-shell nanoparticles, a group of new bi-functional materials that has gain increasing interest in the recent past. Cyclic voltammetry of a large ensemble of such core-shell nanoparticles e.g. magnetic Fe3O4-Au core-shell nanoparticles, distinguishes between intact and imperfect shells, quantifies the ratio of both and estimates the average shell thickness. Since a very large number of nanoparticles can be probed simultaneously and conveniently, it is a powerful complementary method to the established microscopic characterisation of core-shell nanoparticles. vii) The mass transport to and from individual nanoparticles and nanoparticles immobilised on an electrode differ greatly. This altered mass transport can cause an apparent change in the electrochemical reactivity of nanoparticle versus bulk material and likely is the origin of a number of controversial reports in the field of nano-electrocatalysis. Correction of cyclic voltammetry response to account for the altered mass transport at surface immobilised nanoparticles is possible and allows nano-electrocatalytic effects to be resolved. The combination of experiment and theory throughout this project greatly improved our understanding of the interplay of the various parameters involved in the fields of magneto- and nano-electrochemistry. Thus a tool set has been provided to interpret experiments in both fields rigorously by analysing mass transport effects. The relevance of the results of the IMaFECy project is evidenced by a total of 34 articles published in peer-reviewed international journals originating from the research carried out in this project. The findings have further been disseminated in 7 invited lectures and 3 lectures at international conferences that the Fellow (Dr Kristina Tschulik, KT) held in different countries of the European Union for national and international audiences. The active participation in teaching chemistry students of the University of Oxford at an undergraduate level, as well as the supervision of several Master (Part II) students, PhD students and research undergraduate students throughout the project, will have a positive long-term impact on the next generation of chemists. KT’s activity in organising of and participating in various outreach activities and supporting politicians in their decision making, helped to promote a positive image of the European Commission and to reflect the direct socio-economic relevance of the IMaFECy project. In the framework of this Marie Curie Intra European Fellowship a long-term collaboration between the scientist in charge (Prof Richard G Compton) and the Fellow (Dr Kristina Tschulik) has been initiated, together with a number of additional Intra-European and international collaborations, which will have a positive long-term impact on the European Research Area.

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