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Identifier 000452352
Title Development and Characterization of Ni2P/CuCo2S4 Composite Nanostructures for Electrocatalytic Overall Water Splitting
Alternative Title Ανάπτυξη και χαρακτηρισμός σύνθετων νανοδομών Ni2P/CuCo2S4 για ηλεκτροκαταλυτική διάσπαση νερού
Author Μπρά, Σοφία
Thesis advisor Αρματάς, Γεράσιμος
Reviewer Κοπιδάκης, Γεώργιος
Στούμπος, Κων/νος
Abstract The development of highly effective, stable and inexpensive catalysts is an important target in the research of water electrolysis and hydrogen production. A key pursuit of current research efforts is to increase the exposure and accessibility of the catalyst's active sites as well as to improve the kinetics of the reaction. This is achievable by combining suitable chemical components in the same material, which could induce electronic band structure modulation and efficient charge-transfer dynamics, with a properly designed nanostructured morphology, which offers a rich density of active sites and large interfacial contact area. The purpose of this master's thesis is to fabricate and characterize new nanostructured heterostructures of Ni2P and CuCo2S4 composition and to investigate the electrocatalytic activity of these materials towards the electrochemical water splitting and hydrogen evolution reaction (HER). The morphology, composition and crystal structure of the Ni2P/CuCo2S4 composite catalysts were characterized by a combination of electron microscopy, EDS microprobe analysis, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction techniques. These results indicated that Ni2P/CuCo2S4 heterostructures adopt a cubic thiospinel structure and a hexagonal Ni2P phase (in 10-15 nm size), while their surface is endowed with various loadings of nickel phosphide, i.e., 15, 20, 30 and 40 wt.%. Experimental optical absorption, valence band XPS and electrochemical spectroscopy studies coupled with theoretical DFT calculations indicated that p-n Ni2P/CuCo2S4 junctions provide an increased number of electrochemically active surface sites and an efficient interfacial electronic transport with lower resistance, resulting in a remarkable enhancement in the electrocatalytic H2 evolution performance. The unmodified CuCo2S4 sample showed moderate to low electrocatalytic behavior for the hydrogen evolution reaction, giving an overpotential of 348 mV at a current density of 10 mA·cm−2 in an alkaline electrolyte (1M KOH). We show that Ni2P-modification of the CuCo2S4 surface markedly increases the electrochemical activity by improving the transport efficiency of electrons at the Ni2P/CuCo2S4 interface. Thus, the optimized Ni2P/CuCo2S4 catalyst at 30 wt.% Ni2P content reached the lowest overpotential of 183 mV at 10 mA·cm−2 current density under alkaline conditions, which is associated with a 78 mV·dec-1 Tafel slope, indicating a Volmer-Heyrovsky type mechanism. Chronopotensiometric studies revealed that Ni2P/CuCo2S4 is quite stable during the reaction, operating stably for 30 h under a current density of 10 mV·cm−2. In addition, the 30% Ni2P-loaded catalyst showed a very good oxygen evolution reaction (OER) activity with an overpotential of 360 mV at 40 mA·cm−2 current density in 1 M KOH electrolyte. When 30% Ni2P/CuCo2S4 is used as both anode and cathode in a two-electrode electrochemical cell, it requires only a 1.78 V potential for overall water electrolysis under 10 mA·cm−2 current density. Overall, these Ni2P-modified CuCo2S4 catalysts demonstrate great potential for renewable hydrogen production technologies, including water electrolysis.
Language English
Issue date 2022-11-23
Collection   School/Department--School of Sciences and Engineering--Department of Materials Science and Technology--Post-graduate theses
  Type of Work--Post-graduate theses
Permanent Link https://elocus.lib.uoc.gr//dlib/f/c/2/metadata-dlib-1669361101-204569-14297.tkl Bookmark and Share
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