Abstract
An anode bimetallic catalyst comprising Ni-Pd alloy nanoparticles was loaded on acid-treated multi-walled carbon nanotubes (MWCNTs) for application in a direct urea fuel cell. The bimetallic catalyst and MWCNTs were synthesized by a hydrothermal method at 160°C for 5 h. To reduce the catalyst particle size, alkaline resistance, and facilitate their uniform distribution on the surface of the MWCNTs, phosphorus (P) was added to the Ni-Pd/MWCNT catalyst. The effects of P on the distribution and reduction in size of catalyst particles were investigated by Brunauer–Emmett–Teller analysis, transmission electron microscopy, and X-ray diffraction analysis. The enhanced catalytic activity and durability of the P-containing catalyst was confirmed by the high current density [1897.76 mA/cm2 (vs. Ag/AgCl)] obtained at 0.45 V in a 3 M KOH/1.0 M urea alkaline aqueous solution compared with that of the catalyst without P [604.87 mA/cm2 (vs. Ag/AgCl)], as determined by cyclic voltammetry and chronoamperometry. A Urea–O2 fuel cell assembled with a membrane electrode assembly comprising the Ni-Pd(P)/MWCNT catalyst delivered peak power densities of 0.756 and 3.825 mW/cm2 at 25 and 60°C, respectively, in a 3 M KOH/1 M urea solution.
Highlights
Fuel cells are well-known eco-friendly energy production devices that have several advantages (Ryu et al, 2014; Yoon et al, 2014, 2017) such as a high energy-conversion efficiency (Lim et al, 2014; Chen et al, 2017; Yu et al, 2018) that is 70% higher than that of fossil fuel-based energy production systems (Smalley, 2003; Xiao et al, 2015)
This allows the monomeric metal catalysts of Ni and Pd formed at multi-walled carbon nanotubes (MWCNTs) to be more dispersed over the catalytic support and identify the peak of the Ni-Pd catalytic structure, 41.0◦, which is combined in a hetero-dispersive system (Yan et al, 2012; Liu et al, 2017)
The peak at 41.0◦ in the X-ray diffraction (XRD) profile originates from the presence of P that remains on the MWCNT surface after the reduction of metal precursors to metal catalyst; it does not directly affect the catalyst characteristics
Summary
Fuel cells are well-known eco-friendly energy production devices that have several advantages (Ryu et al, 2014; Yoon et al, 2014, 2017) such as a high energy-conversion efficiency (Lim et al, 2014; Chen et al, 2017; Yu et al, 2018) that is 70% higher than that of fossil fuel-based energy production systems (Smalley, 2003; Xiao et al, 2015). The use of single-component Ni catalyst in the operating conditions of urea fuel cells leads to continuous voltage drop and a lower power density than the achievable value This phenomenon is called overpotential in alkaline aqueous solution fuel cells (Kim et al, 2015; Lee et al, 2017a,b), which is the potential difference between the thermodynamically determined reduction potential and the potential at which the reduction reaction occurs. Nano-sized Ni-based metal catalysts have a high surface areato-volume ratio that results in fast catalytic reactions; condensation reduces the surface energy To overcome these problems, highly efficient catalysts with a high catalytic area and improved properties with the catalyst particles distributed evenly over the catalyst support are required (Guo et al, 2015). The addition of P to Ni-Pd prevents the occurrence of overpotential for urea oxidation and increases the active area
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