Ultra-high Seebeck coefficient of a thermal sensor through entropic optimisation of ligand length of Fe(ii) spin-crossover (SCO) materials

Hazirah Che Hassan; Suhana Mohd Said; Nik Muhd Jazli Nik Ibrahim; Megat Muhammad Ikhsan Megat Hasnan; Ikhwan Syafiq Mohd Noor; Rozalina Zakaria; Mohd Faiz Mohd Salleh; Nur Linahafizza Md Noor; Norbani Abdullah

doi:10.1039/d1ra01387d

Ultra-high Seebeck coefficient of a thermal sensor through entropic optimisation of ligand length of Fe(ii) spin-crossover (SCO) materials

RSC Adv. 2021 Jun 14;11(34):20970-20982. doi: 10.1039/d1ra01387d. eCollection 2021 Jun 9.

Authors

Hazirah Che Hassan¹, Suhana Mohd Said¹, Nik Muhd Jazli Nik Ibrahim¹, Megat Muhammad Ikhsan Megat Hasnan², Ikhwan Syafiq Mohd Noor³, Rozalina Zakaria⁴, Mohd Faiz Mohd Salleh¹, Nur Linahafizza Md Noor⁵, Norbani Abdullah⁵

Affiliations

¹ Department of Electrical Engineering, Faculty of Engineering, University of Malaya 50603 Kuala Lumpur Malaysia smsaid@um.edu.my.
² Microelectronic and Nanotechnology - Shamsuddin Research Centre (MiNT-SRC), Faculty of Electrical and Electronic Engineering, University Tun Hussein Onn Parit Raja 86400 Batu Pahat Johor Malaysia.
³ Physics Division, Centre of Foundation Studies for Agricultural Science, University Putra Malaysia 43400 UPM Serdang Selangor Malaysia.
⁴ Department of Physics, Faculty of Science, University of Malaya 50603 Kuala Lumpur Malaysia.
⁵ Department of Chemistry, Faculty of Science, University of Malaya 50603 Kuala Lumpur Malaysia.

Abstract

In this work, we present a spin-crossover (SCO) complex molecular formulation [Fe(L ⁿ )₂](BF₄)₂ in an electrochemical single couple solution. A Seebeck voltage arises when an electrochemical single couple solution is subjected to a temperature difference, resulting in a single couple reaction at either terminal of the electrochemical cell. The ultrahigh Seebeck coefficients were obtained due to a number of molecular optimisation strategies. The [Fe(L¹⁶)₂](BF₄)₂ complex demonstrated a maximum Seebeck coefficient of 8.67 mV K^-1, achieved through a six-pronged approach to maximise entropy during the transition from low spin (LS) to high spin (HS) through: (i) a change in spin state, (ii) a change in physical liquid crystalline state, (iii) the spin Seebeck effect, (iv) the kosmotropic and chaotropic effect, (v) the fastener effect and (vi) thermal heat absorbance. A reduction of the Seebeck coefficient to 1.68 mV K^-1 during the HS-LS transition at higher temperatures is related to the single spin state transition entropy change. In summary, this paper presents a systematic study to identify the contributing factors in the production of a sensor with an ultrahigh Seebeck coefficient for energy harvesting through the optimisation of its molecular entropy elements.