STM 6

Direct measurement of the enthalpy released during Hydrogen adsorption on Ti-decorated graphene

Since its discovery in 2004, research on graphene has achieved remarkable results. In the last years, a huge research effort has been devoted to engineering carbon-based nanomaterials able to adsorb hydrogen molecules with high storage capacity and easy release of them. Monolayer graphene (MLG) represents an appealing material, owing to its favourable physical-chemical properties and its high specific surface area, which makes it ideal for functionalization. Thus, metal-functionalized MLG has been widely investigated both theoretically end experimentally. One of the most promising, and investigated, metals is titanium which has been predicted to allow a gravimetric density of 7.8 wt%, well above DOE prescriptions.

The purpose of our work is to provide a new experimental tool to directly measure the heat released during the hydrogen loading of functionalized graphene. For this purpose, a sensitive gold film thermometer has been realised. The gold film deposited on a Si wafer acts as temperature probe and sample holder for MLG (Fig. 1), with dimensions of about 5 mm x 5 mm. Thermometric measurements are performed monitoring its resistance variation with temperature. The MLG is grown by CVD method on a copper foil and successively transferred on the thermometer. Samples’ quality has been checked with Raman spectroscopy. Gold surface has been characterized by Scanning Tunnelling Microscopy before and after graphene transfer. After a careful thermometer characterization and calibration, a thermal signal during hydrogen loading has been detected (Fig. 2). These results represent the first direct measurements of Enthalpy (H_r) released during hydrogen loading process in functionalized graphene. In two successive experiments, temperature increases of Delta T = 0.065 K and Delta T = 0.25 K have been measured, corresponding to H_r = (23.2 ± 4.7) uJ and H_r = (58 ± 12) uJ. Each measurement has been cross-checked through Temperature Desorption Spectroscopy (TDS), extracting the loaded hydrogen amount and the binding energy using the Redhead equation. TDS spectra (Fig. 3) gave an average binding energy E_b = (1.32 ± 0.07) eV/molecule and a desorbed hydrogen amount of N = (9.77 ± 0.10) x 10^13 molecules, which corresponds to H_r = (20.6 ± 1.3) uJ for the first experiment. Similarly, we obtain E_b = (1.24 ± 0.09) eV/molecule and N = (2.57 ± 0.03) x 10^14 molecules, which correspond to H_r = (51.0 ± 4.3) uJ, for the second exposure. Results are in good agreement with thermometric measurements. This represents the first direct measurement of heat release in metal-decorated graphene during hydrogen adsorption.


Figure 4: (a) STM image from a gold thermometer sample on mica after a heating ramp to 200C. The image shows the corrugation lines typical for the gold surface herringbone reconstruction. Image size: 80 nm x 80 nm. (b) Response of the two sensors (gold-on-mica and gold-on-Si) to illumination with a lamp for 60 seconds.

However, a limitation of the thermometer is the surface roughness, which does not allow atomic resolution with the STM probe. Therefore, we have developed an upgraded version based on an atomically flat, monocrystalline gold film thermometer on mica substrate. As shown in Fig. 4(a), gold recrystallization is obtained inside the STM chamber, allowing the successive investigation of the thermometer surface by LEED and with STM imaging. Large gold terraces allow achieving a resolution comparable with atomic dimensions during STM imaging of the surface. Moreover, the gold-on-mica thermometer performs about 10 times better than the previous sensor based on a Si substrate, see Fig. 4(b). This work opens the possibility to investigate simultaneously energy (heat) exchange mechanisms and surface physics with the same physical support, providing a unique perspective in understanding physics and chemistry at the nanoscale.

Publications:

  1. Luca Basta: A calorimetric study of hydrogen storage on graphene functionalized with Titanium, Master Thesis, University of Pisa, Italy, 2016 – 2017.
  2. Luca Basta, S. Veronesi, Y. Murata, Z. Dubois, N. Mishra, F. Fabbri, C. Coletti, and S. Heun: A sensitive calorimetric technique to study energy (heat) exchange at the nano-scale, arXiv:1904.12544 [physics.chem-ph].
  3. Luca Basta, S. Veronesi, Y. Murata, Z. Dubois, N. Mishra, F. Fabbri, C. Coletti, and S. Heun: A sensitive calorimetric technique to study energy (heat) exchange at the nano-scale, Nanoscale 10 (2018) 10079.
  4. Thea Papa: An atomically flat gold film thermometer on mica for calorimetric applications, Master Thesis, University of Pisa, Italy, 2017 – 2018.
  5. Stefano Veronesi, Thea Papa, Yuya Murata, and Stefan Heun: An atomically flat single-crystalline gold film thermometer on mica to study energy (heat) exchange at the nano-scale, arXiv:1911.00283 [physics.app-ph].
  6. S. Veronesi, T. Papa, Y. Murata, and S. Heun: An atomically flat single-crystalline gold film thermometer on mica to study energy (heat) exchange at the nano-scale, Appl. Surf. Sci. 512 (2020) 145658. [Free Link]
  7. Valentina Tozzini and Stefano Veronesi: Graphene engineering: new opportunities for controlled functionalization and energy storage, CNR Nano Activity Report 2020 [Page 66].

Presented at:

  1. Luca Basta: A calorimetric study of hydrogen storage on graphene functionalized with Titanium, Thesis Defense, University of Pisa, Italy, 26 June 2017. [Talk]
  2. S. Veronesi, Luca Basta, Y. Murata, N. Mishra, C. Coletti, S. Heun: Direct measurement of the enthalpy released during Hydrogen adsorption on Ti-decorated graphene, Graphene Week, Athens, Greece, 25 – 29 September 2017 (poster). [Abstract] [Poster]
  3. Luca Basta, S. Veronesi, Y. Murata, N. Mishra, C. Coletti, and S. Heun: A calorimetric study of hydrogen storage on graphene functionalized with Titanium, University of Seoul, S. Korea (Prof. Jeil Jung), 18 September 2017 (invited). [Abstract] [Talk]
  4. Stefano Veronesi: A sensitive calorimetric technique to study energy (heat) exchange at the nano-scale, CNR Nano Colloquium, Pisa, Italy, 19 April 2018. [Abstract] [Talk]
  5. Thea Papa: An atomically flat gold film thermometer on mica for calorimetric applications, Master Thesis Defense, Università di Pisa, Pisa, Italy, 20 July 2018. [Talk]
  6. Luca Basta, S. Veronesi, Y. Murata, Z. Dubois, N. Mishra, F. Fabbri, C. Coletti, and S. Heun: A novel sensitive calorimetric technique to study energy (heat) exchange at the nano-scale, European Conference on Surface Science ECOSS34, Aarhus, Denmark, 26-31 August 2018 (oral). [Abstract] [Talk]
  7. S. Veronesi, Luca Basta, T. Papa, Y. Murata, Z. Dubois, N. Mishra, F. Fabbri, C. Coletti, and S. Heun: An atomically flat, single-crystal, gold film thermometer on mica to study energy (heat) exchange at the nano-scale, Nanoinnovation 2018, Rome, Italy, 11-14 September 2018 (invited). [Abstract] [Talk]
  8. S. Veronesi, Luca Basta, Y. Murata, Z. Dubois, N. Mishra, F. Fabbri, C. Coletti, and S. Heun: Sensing energy (heat) exchange at the nano-scale during H2-uptake on Ti-functionalized graphene, Materials.it 2018, Bologna, Italy, 22-26 October 2018 (oral). [Abstract] [Talk]
  9. S. Veronesi, Luca Basta, T. Papa, Y. Murata, Z. Dubois, N. Mishra, F. Fabbri, C. Coletti, and S. Heun: An atomically flat, monocrystalline, gold film thermometer on mica to study energy (heat) exchange at the nano-scale, NanoMeeting 2018, Pisa, Italy, 29 – 30 October 2018 (poster). [Abstract] [Poster]
  10. Luca Basta, S. Veronesi, T. Papa, Y. Murata, Z. Dubois, N. Mishra, F. Fabbri, C. Coletti, and S. Heun: Investigating simultaneously energy (heat) exchange and surface physics on samples at the nanoscale, FisMat 2019, Catania, Italy, 30 September – 4 October 2019 (oral). [Abstract] [Talk]
  11. Stefano Veronesi, Luca Basta, Thea Papa, Zoé Dubois, Neeraj Mishra, Filippo Fabbri, Camilla Coletti, Yuya Murata, Stefan Heun: Bridging heat exchange and surface physics investigations on samples at the nano-scale, XLII National Conference on Calorimetry, Thermal Analysis and Applied Thermodynamics, Online, Udine, Italy, January 27 – 28, 2021 (oral). [Abstract] [Talk]