Ni-Pt Core-Shell Formation via Spontaneous Galvanic Displacement Reaction at Boron Doped Diamond Electrodes for Ammonia Oxidation Reaction

Abstract

Ammonia is a major environmental pollutant that is highly toxic and may cause unfavourable effects to the human body, even in low concentrations. As a result, the monitoring and elimination of NH3 has been an important topic worth exploring in depth. Moreover, ammonia can be a suitable fuel cell source because its theoretical electrical charge density is relatively high and it’s possible to take this advantage by converting ammonia to nitrogen and electrical energy via the ammonia oxidation reaction (AOR). This reaction requires a catalyst to decrease the energy barrier that prevents the molecule from reacting and transforming into nitrogen.Ammonia electro-oxidation reaction has been paid much attention in recent years because it is widely used in various fields. However, the electro-oxidation of ammonia is a complex process, especially the reaction intermediate has a slow toxic effect on the electrode. To reduce the catalyst poisoning by the absorption of intermediate, the constituent and structure of the catalysts must be deeply researched.Herein, a bimetallic Pt–Ni catalyst-modified boron-doped diamond (BDD) electrode was done via spontaneous galvanic displacement reaction for the ammonia oxidation reaction. The synergistic properties may include the promotion of low-temperature oxidation, improvement of the oxidation resistance, and increased catalytic efficiency. BDD was used as the electrode substrate in this work due to its excellent resistance to corrosion and good stability over time in a highly corrosive environment. First, nickel was electro-deposited through chronoamperometry on the BDD electrode surface at a potential of -1.1V vs Ag/AgCl in 0.1M KClO4 & 5mM Ni (NO3)2.6H2O aqueous solution. Second, platinum was deposited on the nickel particles on the BDD electrode surface through a spontaneous galvanic displacement reaction by a redox process which involves the nickel oxidation and Pt2+ reduction, using a K2PtCl4 precursor on the BDD surface while forming a core shell structure. Lastly, the Pt-Ni deposited on the BDD surface was then characterized through different techniques such as XPS, SEM, EDS, and Raman before and after the ammonia oxidation reaction.Preliminary studies of the behaviour of BDD electrodes in the presence of Ni and Pt have been carried out to determine the electrochemical conditions at which the substrate works with these metal salts. The results found with these studies will show how Pt-Ni catalyst will improve AOR in alkaline media.