Titanium Nanotubes as an Effective Electrocatalyst Support for Hydrogen Evolution Reaction
Authors: Alaqad Khaled M. , Kandiel Tarek A. , Basheer Chanbasha 
Published: February 2024

Developing proper support for hydrogen evolution reaction (HER) electrocatalysts is important for enhancing the HER efficiency and reducing the cost of green hydrogen production. TiO2-based-catalyst support has attracted considerable attention due to its commercial availability, high stability, low cost, and its unique electronic and ionic properties [1]. TiO2 is commonly utilized in various applications involving, photocatalysis, solar cells, and photoelectrochemical water splitting [2]. The ease of the synthesis of TiO2 with different morphologies and crystal structures makes it promising support to replace carbon in electrochemical applications [3]. Recently, anatase TiO2 nanoparticles decorated with PtOx clusters showed benchmark activity toward hydrogen evolution from the acidic medium with an overpotential of –125 mV at –10 mA cm–2 [4]. Furthermore, Pt clusters supported on porous TiO2 nanoparticles achieved higher stability compared with that of the benchmark Pt/C catalyst due to the facile electron transfer from TiO2 to PtOx [4]. Despite the TiO2-supported Pt nanoclusters have been recently investigated, the characteristic of HER electrocatalysts loaded on highly ordered TiO2 nanotube arrays (TNTs) is still unexplored. TNTs are expected to be an optimal support architecture owing to their large internal surface area and excellent electron mobility [5, 6]. Moreover, they can be readily synthesized and have robust mechanical stability. Therefore, in our work, highly ordered TNTs on Ti substrate have been synthesized and investigated as a support for different types of HER electrocatalysts (i.e. PtOx [7], MoS2 [8], and CoOP [9]). The PtOx clusters supported on TNTs (Ti/TNTs/PtOx) showed excellent performance for HER. An overpotential of –30 mV was sufficient to deliver –10 mA cm–2 from the acidic medium. The electrocatalytic mass activity of Ti/TNTs/PtOx (i.e. 204 mA mgPt
–1) is enhanced by 12 and 1.7-fold compared to those of Pt/C and titanium nanoparticles (TNPs) supported PtOx electrocatalysts, respectively. The superior activity of the Ti/TNTs/PtOx is mainly due to its large electrochemically active surface area and the excellent electron mobility in the TNTs support. The immobilizing of MoS2 on TNTs resulted in enhanced electrocatalytic HER activity. An overpotential of –200 mVRHE was ample to deliver –10 mA cm–2 from 0.5 M H2SO4 aqueous solution. A synergy between the in-situ immobilized MoS2 and TNTs is proposed to explain the enhanced HER performance. In an alkaline medium, the Ti/TNTs/CoOP electrode fabricated by incorporating CoOP spheres into the TNTs exhibited only –130 mV overpotential to deliver –10 mA cm–2. This value is superior to that of CoOP deposited on bare Ti foil (–165 mV), FTO (–185 mV), and glassy carbon (–214 mV). In general, our study revealed that the TNTs support improves the electrochemical surface area and accessibility of active sites while reducing the charge transfer resistance at the electrode/electrolyte interface.

Acknowledgments

T.A.K. thanks the Deanship of Research Oversight and Coordination at KFUPM for the conference attendance support.

References

[1] M.M. Khan, S.A. Ansari, D. Pradhan, M.O. Ansari, J. Lee, M.H. Cho, Band gap engineered TiO2 nanoparticles for visible light induced photoelectrochemical and photocatalytic studies, J. Mater. Chem. A, 2 (2014) 637-644.

[2] J. Schneider, M. Matsuoka, M. Takeuchi, J. Zhang, Y. Horiuchi, M. Anpo, D.W. Bahnemann, Understanding TiO2 Photocatalysis: Mechanisms and Materials, Chem. Rev., 114 (2014) 9919-9986.

[3] N. Cheng, S. Stambula, D. Wang, M.N. Banis, J. Liu, A. Riese, B. Xiao, R. Li, T.-K. Sham, L.-M. Liu, G.A. Botton, X. Sun, Platinum single-atom and cluster catalysis of the hydrogen evolution reaction, Nature Commun., 7 (2016) 13638.

[4] X. Cheng, Y. Li, L. Zheng, Y. Yan, Y. Zhang, G. Chen, S. Sun, J. Zhang, Highly active, stable oxidized platinum clusters as electrocatalysts for the hydrogen evolution reaction, Energy Environ. Sci., 10 (2017) 2450-2458.

[5] C. Richter, C.A. Schmuttenmaer, Exciton-like trap states limit electron mobility in TiO2 nanotubes, Nature Nanotechnology, 5 (2010) 769.

[6] P. Li, H. Hu, J. Xu, H. Jing, H. Peng, J. Lu, C. Wu, S. Ai, New insights into the photo-enhanced electrocatalytic reduction of carbon dioxide on MoS2-rods/TiO2 NTs with unmatched energy band, Appl. Catal. B: Environ., 147 (2014) 912-919.

[7] K.M. AlAqad, T.A. Kandiel, C. Basheer, TiO2 Nanotubes Supported PtOx Nanoclusters with Enhanced Mass Activity for Electrocatalytic Hydrogen Evolution, ChemCatChem, 12 (2020) 1-10.

[8] K.M. AlAqad, T.A. Kandiel, C. Basheer, Synergy between in-situ immobilized MoS2 nanosheets and TiO2 nanotubes for efficient electrocatalytic hydrogen evolution, Int. J. Hydrogen Energy, 47 (2022) 2366-2377.

[9] K.M. AlAqad, T.A. Kandiel, T. N. Jahangir, M. Qamar, C. Basheer, TiO2 Nanotubes modified with Cobalt Oxyphosphide Spheres for Efficient Electrocatalytic Hydrogen Evolution Reaction in Alkaline Medium, Electrochimica Acta, (2023), accepted.