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Nickel based nanoalloys as reduction electrocatalysts for solar fuel production

Pridmore, Natalie Estelle (2015) Nickel based nanoalloys as reduction electrocatalysts for solar fuel production. PhD thesis, University of York.

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Abstract

In order to optimise the efficiency of solar fuel devices, development of cheap, active and stable reduction electrocatalysts for solar fuel production is crucial. To this end, ligand stabilised nickel nanoalloys of around 10 nm with relatively small size distributions, have been synthesised for a variety of compositions utilising first row transition metals (Cr, Fe, Co and Cu). Bi- and trimetallic nanoalloys have been synthesised and good control over composition was demonstrated. Synthesised nanoalloys were electrochemically tested to assess their proton and CO2 reduction activities. All nanoalloys showed higher hydrogen evolution reaction (HER) activity than pure nickel. For bimetallic nanoalloys, in pH 1, a general increase in HER activity with increased electron negativity was observed. The Ni0.5Cu0.3Co0.2 nanoalloy showed the highest HER activity at pH 1, whereas the Ni0.5Co0.3Fe0.2 nanoalloy was most active for HER in pH 13. Little difference between the activities for all nanoalloys was observed at pH 7. The nanoalloys showed differing selectivity’s for CO2 reduction products. Solution based CO2 reduction products were detected at low overpotentials (below -0.789 V vs RHE, pH 6.8), although low faradaic efficiencies (< 1%) were observed. High resolution scanning electron microscopy (HR-SEM) was used to attempt to analyse the nanoalloys after deposition onto the electrodes and after electrochemical testing. The results indicated the presence of sub-monolayer coverage, therefore increasing the nanoalloy coverage without large amounts of agglomeration occurring could result in the observation of higher current densities at lower overpotentials. The stability of the nanoalloy electrodes was also investigated and no decrease in HER activity was observed over 12 hours at -0.5 V vs RHE. Moreover, repeated cycling resulted in an increase in activity being observed. This may be due to leaching of elements overtime. A procedure has been developed using a range of techniques to analyse nanoalloy composition, test proton and CO2 reduction activities and assess stability. This has not only allowed for direct comparison between different materials studied, it also provides a framework for future investigations of nanoalloys for (photo)electrochemical proton and CO2 reduction.

Item Type: Thesis (PhD)
Keywords: Electrocatalyst, Nanoalloy, Nanoparticle, Nickel, Solar Fuel, Reduction, CO2, Hydrogen
Academic Units: The University of York > Chemistry (York)
Identification Number/EthosID: uk.bl.ethos.680623
Depositing User: Miss Natalie Estelle Pridmore
Date Deposited: 29 Feb 2016 11:56
Last Modified: 08 Sep 2016 13:33
URI: http://etheses.whiterose.ac.uk/id/eprint/11976

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