Periodic Reporting for period 1 - MONMETAL (Generation of monolayer thin 2D nanosheets of noble/semi-noble metals: Investigation of their structural, electronic and catalytic properties )
Berichtszeitraum: 2018-06-01 bis 2020-05-31
The movement of electrolyte solutions within nanometer-scale channels is central to understanding nanofluidic phenomena. Ion transport within small (nm) scale pores is also key to electrochemical energy storage, where the energy storage process is dependent on ionic ingress into porous carbon materials [1,2]. Although very significant advances in the understanding of ion movement within electrically charged pores have been made [3], a key barrier is that porous carbon materials contain a complex distribution of interconnected pores of varying size, making it difficult to de-convolute specific size effects. A further connection between the fields of nanofluidics and electrochemistry arises because electrochemical control, based on the phenomenon of electrowetting, may be used to drive liquids into small channels [4]. This restriction has been overcome by applying the nanochannel technology developed by Radha et al [5,6] in the electrochemical context, where one “wall” of the graphene channel is used as an electrode. We are therefore able to observe the effects of differing ion sizes on electrical double-layer capacitance, additionally, the effects of such extreme confinement on electrochemical processes (both capacitive and Faradaic) can also be discerned.
References:
1. B.E. Conway, Electrochemical Supercapacitors, Springer, 1999.
2. Z. Chen et al, Adv. Mater., 23, (2011), 791
3 J. Chmiola, G. Yushin, Y. Gogotsi, C. Portet, P. Simon, P.L. Taberna, Science, 313, (2006), 1760
4 D.J. Lomax et al, Soft Matter, 12, (2016), 8798.
5 B. Radha et al, Nature, 538, (2016), 222
6 A. Esfandiar et al, Science, 358, (2017), 511
References:
1. B.E. Conway, Electrochemical Supercapacitors, Springer, 1999.
2. Z. Chen et al, Adv. Mater., 23, (2011), 791
3 J. Chmiola, G. Yushin, Y. Gogotsi, C. Portet, P. Simon, P.L. Taberna, Science, 313, (2006), 1760
4 D.J. Lomax et al, Soft Matter, 12, (2016), 8798.
5 B. Radha et al, Nature, 538, (2016), 222
6 A. Esfandiar et al, Science, 358, (2017), 511
The work done in this project addressed the capacitance of the ions such as potassium, sodium, chloride in the ultimate confinement of the size of the ions themselves. It was found that the faradaic contributions to the ionic capacitance are dominant due to the participation of the edges of the channels which are roughened by plasma exposure. To circumvent this problem, a monolayer graphene was overlaid onto the channels and hence capacitive effects of the ions could be deciphered. This is a new development in the fabrication methodology of capillaries.
The Fellow successfully adapted the angstrom capillaries [5] to measure the electrochemical capacitance of ions. For this the electrode in contact with the graphene on capillaries should not be in direct contact with the electrolyte. This was made possible by use of a photoresist polymer which acts as an insulating encapsulant for the capillaries. Various coated layers such as polymethyl methacrylate, dielectric halfnium oxide, silicon nitride, oxide were experimented before finalizing the photoresist coating. Out of all the layers investigated, photoresist could sustain the electrochemical measurement conditions with minimal degradation.
The Fellow successfully adapted the angstrom capillaries [5] to measure the electrochemical capacitance of ions. For this the electrode in contact with the graphene on capillaries should not be in direct contact with the electrolyte. This was made possible by use of a photoresist polymer which acts as an insulating encapsulant for the capillaries. Various coated layers such as polymethyl methacrylate, dielectric halfnium oxide, silicon nitride, oxide were experimented before finalizing the photoresist coating. Out of all the layers investigated, photoresist could sustain the electrochemical measurement conditions with minimal degradation.
1. The project has increased the understanding of ion capacitance dependence on the pore sizes in which the ions are present.
2. The project has produced the architecture of capillaries to probe ion capacitance with control over all dimensions in a precise fashion while avoiding the faradaic contributions to the capacitance for the first time.
2. The project has produced the architecture of capillaries to probe ion capacitance with control over all dimensions in a precise fashion while avoiding the faradaic contributions to the capacitance for the first time.