Oxidation of ammonia using PtRh/C electrocatalysts: Fuel cell and electrochemical evaluation

Abstract

Júlio César Martins Silva)Highlights Direct ammonia fuel cell (DAFC) performance using PtRh/C electrocatalysts as anode.Ammonia oxidation evaluation by electrochemical experiments. An optimization study of the NH 4 OH and KOH concentrations used as fuel in a DAFC.Using PtRh/C 90:10 were obtained the highest power density and open circuit voltage.Using 3 mol L -1 KOH and 3 mol L -1 NH 4 OH the best result in a DAFC was obtained. AbstractThis study reports on the use of PtRh/C electrocatalysts prepared by the borohydride reduction method with different Pt:Rh atomic ratios: (90:10, 70:30 and 50:50) which was investigated toward the ammonia electro-oxidation considering electrochemical and also direct ammonia fuel cell (DAFC) experiments. The DAFC experiments were conducted using different proportions of NH 4 OH and KOH as fuels.X-ray diffraction showed the formation of PtRh alloy while transmission electron micrographs showed the particles sizes between 4.1 and 4.5 nm. Among the different NH 4 OH and KOH concentrations the combination of 3 mol L -1 NH 4 OH and 3 mol L -1 KOH was the most favorable due to the higher KOH concentration, which increased the electrolyte conductivity, thus improving the ammonia oxidation. Moreover, among the PtRh/C electrocatalysts the Pt:Rh ratio of 90:10 showed to be the best suited one since it showed a power density almost 60 % higher than Pt. X-ray photoelectron spectroscopy results revealed for this catalyst that the nanoparticles contain a high proportion of metallic Pt and Rh phases, supporting the alloy formation between Pt and Rh. The improved fuel cell efficiency can be related to the combination of different effects: the alloy formation between Pt and Rh (electronic effect), suppressing the adsorption strength of poisonous intermediates, and a synergic effect between Pt and Rh at this composition.

Rhodium Nanoparticle-Loaded Carbon Black Electrocatalyst for the Glycerol Oxidation Reaction in Alkaline Medium

“…The Rh3d, Pt4f, Pd3d and Au4f core level spectra for Rh/CB, Pt/CB, Pd/CB and Au/CB are shown in Figure 1(b), respectively. For Rh/CB, the Rh3d spectrum contained doublets assigned to the 3d 5/2 and 3d 3/2 peaks of metallic Rh and small shoulders assigned to Rh 2 O 3 at higher binding energies [24]. For the other catalysts, each core level spectrum contained doublets assigned to metallic Pt, Pd or Au.…”

Evaluation of carbon supported platinum–ruthenium nanoparticles for ammonia electro-oxidation: Combined fuel cell and electrochemical approach

“…DAFC offers an important alternative to the current energy generation systems as clean and carbon-free fuel for efficient power source [4,10,11]. Ammonia has low production cost, is easy to handle and to transport [2,11], furthermore, the theoretical charge for ammonia oxidation to N 2 is 4.75 Ah g À1 that is very close to theoretical charge of methanol, 5.02 Ah g À1 , in its oxidation to CO 2 [2].…”

“…DAFCs experiments were conducted using 1 M (NH 4 OH þ KOH) as already described in details elsewhere [3,4,10,18]. In these experiments, a single cell set at 50 C with an electrode area of 5 cm 2 was employed.…”

“…For all experiments, a commercial Pt/C (BASF) with 20 wt% of metals loading was used as cathode. A Nafion ® 117 membrane previously exposed to 6 mol L À1 KOH for 24 h [3,4,10,26] was used for fuel cell experiments.…”

“…In order to overcome the deactivation of platinum by poisoning reaction intermediates and to increase the current density of AmER, Pt-binary electrocatalysts have been reported in the literature, such as PtIr [2,5,12,15,17], PtPd, PtSnO x [2,17], PtRh [2,4,5], PtNi [15] and PtRu [2,11,15]. It is well known that different factors, e.g., nanoparticle synthesis method, particle size, particle size distribution, surface and bulk structure, catalyst support, etc.…”