Synthesis and Characterization of Ordered Cobalt Phosphide Nanowire Arrays As a Potential Catalyst for HER/Oer Reactions.
Authors: Bogusz Joanna , Palowska Renata , Zaraska Leszek , Kozieł Marcin , Gajewska Marta , Liu Lifeng , Sulka Grzegorz Dariusz , Brzozka Agnieszka 
Published: December 2020

Nowadays, increased interest in the field of nano-scale materials is observed [1]. Knowledge about the physicochemical properties of nano-objects is desirable since they exhibit completely different properties than their macroscopic counterparts. The greatest advantage of nanomaterials is their developed specific surface area. This feature is useful in many fields of science, e.g., catalysis, that uses a large number of active centers (resulting from the developed surface), as well as modifications of the electronic structure of nanoparticles that change their redox properties.

For many years, an effective evolution of hydrogen, which is recognized as a zero-emission fuel, has been a problem. The gaseous hydrogen can be obtained via a very important reaction of water decomposition. In this field, developing a catalyst that enables low-cost, efficient, and fast water lysis is the main challenge. One of the potential catalysts for an electrochemical water decomposition is the cobalt phosphide [2], which can be obtained via the phosphorization of cobalt. Undoubtedly, the application of the cobalt phosphide nanowire arrays electrode will be beneficial due to the large surface area.

In this study, an attempt to the electrodeposition of cobalt nanowires using two types of baths (i.e., aqueous and non-aqueous), via constant current and constant potential modes at different temperature ranges was made. Thus, the influence of these factors on the surface morphology of the obtained nanowires as well as their growth rate was investigated. The cobalt phosphide nanowires were obtained via annealing of the Co nanowires inside the AAO (anodic aluminum oxide) membranes, with red phosphorus in an inert atmosphere at 500 ºC for 2 h. The morphology and chemical composition of cobalt and cobalt phosphide nanowires were examined using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). Electrochemical tests were carried out in a three-electrode cell using 0.5 M H2SO4 as an electrolyte. For all experiments, except XRD, the AAO templates were removed in 1 M NaOH.

[1] Baer, D. R., Engelhard, M. H., Johnson, G. E., Laskin, J., Lai, J., Mueller, K., Moon, D. Surface characterization of nanomaterials and nanoparticles: Important needs and challenging opportunities, Journal of vacuum science & technology, 2013, 31(5), 50820

[2] Pan, Y.& Lin, Y. & Chen, Y. & Liu, Y. & Liu, C., Cobalt phosphide-based electrocatalysts: Synthesis and phase catalytic activity comparison for hydrogen evolution, Journal of Materials Chemistry A., 2016, 4(13), 4745-4754

This work was supported by the National Science Centre Poland (Grant No. 2017/26/M/ST5/00715). The participation in this conference was made possible by financial support from the Polish Ministry of Science and Higher Education within a conceptual non-competitive project entitled "Best of the best! 4.0." (Measure 3.3). The project is co-financed from the European Social Fund under the Operational Programme Knowledge, Education, Development 2014-2020 (POWR.03.03.00-00-P019/18).