Sains Malaysiana 49(12)(2020): 3117-3123

http://dx.doi.org/10.17576/jsm-2020-4912-24

Cobalt Sulfide as Photoelectrode of Photoelectrochemical Hydrogen Generation from Water

(Kobalt Sulfida sebagai Fotoelektrod untuk Penjanaan Hidrogen Fotoelektrokimia daripada Air)

MUSTAFID AMNA RAMBEY¹, KHUZAIMAH ARIFIN¹*, LORNA JEFFERY MINGGU¹ & MOHAMMAD B. KASSIM^1,2

¹Fuel Cell Institute, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor Darul Ehsan, Malaysia

²School of Chemistry Sciences and Food Technology, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor Darul Ehsan, Malaysia

Received: 6 August 2020/Accepted: 11 September 2020

ABSTRACT

This study aimed to synthesize and characterize cobalt sulfide deposited on FTO by hydrothermal method and investigate its photoelectrochemical (PEC) water splitting performance. Cobalt sulfide thin films were produced by annealing at two different temperatures, namely, 400 and 500 °C. X-ray diffraction (XRD) and Fourier transform Raman spectroscopy were used to characterize the phase structure. Scanning electron microscopy was used to observe the morphology. Ultraviolet-visible spectroscopy and linear sweep voltammetry analyses were used to determine the thin-film band gap and evaluate the PEC water splitting performance, respectively. From the XRD and Raman analyses, all the samples produced consisted of mixed phases of Co₃S₄ and Co₉S₈. However, each sample contained different percentage phases. The sample annealed at 400 °C contained more Co₉S₈, whereas that annealed at 500 °C contained comparable amounts of Co₃S₄ and Co₉S₈. The morphologies of pre-annealed samples showed vertical flakes with diameters around 200-250 nm and flake thickness around 25-50 nm. When the temperature was increased from pre-annealing temperature to 400 and 500 °C, several flakes were destructed and formed spherical-like clusters. The Tauc plot from absorption analysis showed that the samples annealed at 400 and 500 °C produced similar band gaps at ~2.0 eV. The PEC performance analysis results show that annealing at 400 °C produced the highest photocurrent density of 10 µA/cm² at a potential of -0.7 V.

Keywords: Cobalt sulphide; hydrogen production; hydrothermal; photoelectrochemical

ABSTRAK

Kajian ini bertujuan untuk mensintesis dan mencirikan kobalt sulfida yang dimendapkan pada FTO dengan kaedah hidrotermal dan mengkaji keupayaannya untuk pemisahan air fotoelektrokimia (PEC). Filem nipis kobalt sulfida yang terhasil disepuhlindap pada dua suhu yang berbeza, iaitu: 400 dan 500 °C. Analisis pembelauan sinar-X (XRD) dan spektroskopi transformasi Fourier Raman (Raman) digunakan untuk mencirikan struktur fasa. Mikroskopi elektron imbasan (SEM) digunakan untuk memerhatikan morfologi. Analisis spektroskopi ultraungu-nampak (UV-Vis) dan voltametri kilasan linear digunakan untuk menentukan sela jalur dan menilai prestasi pemisahan air PEC filem nipis tersebut. Daripada analisis XRD dan Raman, semua filem nipis yang dihasilkan terdiri daripada fasa campuran Co3S4 dan Co9S8. Walau bagaimanapun, filem nipis tersebut berisi peratusan fasa yang berbeza. Filem nipis yang disepuhlindap pada suhu 400 °C berisi lebih banyak Co9S8, sedangkan yang disepuhlindap pada 500 °C berisi jumlah Co3S4 dan Co9S8 yang lebih berimbang. Morfologi sampel pra-sepuhlindap menunjukkan kepingan menegak dengan diameter ̴ 200-250 nm dan ketebalan ̴ 25-50 nm. Selepas suhu dinaikkan daripada suhu pra-sepuhlindap kepada 400 dan 500 °C, beberapa kepingan hancur dan membentuk gumpalan seperti sfera. Plot Tauc daripada analisis penyerapan menunjukkan bahawa filem nipis disepuhlindap pada suhu 400 dan 500 °C menghasilkan sela jalur yang hampir sama ̴ 2.0 eV. Hasil analisis prestasi PEC mendapati bahawa filem nipis disepuhlindap pada suhu 400 °C mempunyai ketumpatan arus tertinggi sebesar 10 μA/cm2 pada potensi -0,7 V vs Ag/AgCl.

Kata kunci: Fotoelektrokimia; hidroterma; kobalt sulfida; pengeluaran hydrogen

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*Corresponding author; email: khuzaim@ukm.edu.my