Synthesis of Platinum Nanoparticles by Plasma Sputtering onto Glycerol: Effect of Argon Pressure on Their Physicochemical Properties

Abstract

Electrochemical energy conversion devices, such as polymer electrolyte membrane fuel cells (PEMFCs) and PEM electrolyzers are considered as possible candidates for integration in future renewable energy network 1,2 . However, the oxygen reduction reaction (ORR) kinetic at the cathode of a PEMFC is slow and the overpotential at the cathode is generally high (higher than 0.200 V), whereas that of the hydrogen oxidation at the anode is ca. 0.050 V 3 . For this purpose, platinum (Pt) or its alloys are often required as electrocatalyst because of their excellent catalytic activity for the ORR 4 . Electrocatalysis involves surface reactions, therefore, a high surface/inner atoms ratio is desirable to improve the Pt nanoparticles (Pt NPs) performance. NPs with size ranging between 2 to 4 nm are generally preferred 5 .NPs can be obtained through various physical, chemical or physicochemical routes 6,7 . The chemical methods are very versatile in terms of controlling NPs shape and size by varying the reaction conditions. However, NPs chemical synthesis requires additives, which generate by-products difficult to remove and NPs with limited purity. In contrast, physical methods (such as sputtering, thermal evaporation, laser ablation, spark discharge…) on solid substrates avoid the use of additives, allowing the production of pure metallic NPs with the same material composition as that of the starting material. Moreover, these methods can be considered as green approaches using non-toxic reducing agents and avoiding the formation of byproducts 8 . Among physical techniques for preparing electrocatalytic NPs, magnetron sputtering is known to produce efficient Pt NPs deposited on a microporous carbon layer 9 or on a polymer electrolyte membrane 10 to directly fabricate the catalytic layer composite. However, using the sputtering method for the deposition of metal NPs onto such substrates often makes the control of the NPs properties (size, dispersion and morphology) complex. Moreover, this process makes also difficult to create three phase boundaries by the addition of ionomer in comparison with the conventional liquid ink preparation techniques based on classical chemical processes for carbon supported NPs. A solution consists in synthesizing NPs directly in a liquid phase using magnetron sputtering technique and to disseminate the NPs onto a porous substrate. This innovative method

Insights on the Formation of Nanoparticles Prepared by Magnetron Sputtering Onto Liquids: Gold Sputtered Onto Castor Oil as a Case Study

“…However, some scientists reported an increase in the NP size with discharge voltage (Suzuki et al, 2009;Wender et al, 2010Wender et al, , 2011Sugioka et al, 2015). This behavior might be explained by the heating of the host liquid by plasmaborn species and sputtered metal atoms and the IR radiations emitted by the target during the deposition (Orozco-Montes et al, 2021). For example, it has been recently shown that the temperature of 4 ml of glycerol was increased by 17°C during 20 min platinum deposition with 12 cm of working distance (100 W; 5 W/cm 2 ) and by 40°C with 5 cm of working distance at the same DC power density (Orozco-Montes et al, 2021).…”

“…This behavior might be explained by the heating of the host liquid by plasmaborn species and sputtered metal atoms and the IR radiations emitted by the target during the deposition (Orozco-Montes et al, 2021). For example, it has been recently shown that the temperature of 4 ml of glycerol was increased by 17°C during 20 min platinum deposition with 12 cm of working distance (100 W; 5 W/cm 2 ) and by 40°C with 5 cm of working distance at the same DC power density (Orozco-Montes et al, 2021). An increase in liquid temperature leads to a decrease in both the viscosity and surface tension of the host liquid, so that the sputter atoms more easily penetrate under the liquid surface and the number of collisions between freshly solvated sputtered atoms and primary clusters formed under the liquid surface increases.…”

“…The size of NPs was measured by TEM 10 months after the sputtering procedure; it was found that the mean diameter of the final Au NPs does not depend on gas pressure (see Figures 4D-I). The effect of argon pressure on metal NP size obtained by sputtering onto liquids has been already studied in three works (Wagener et al, 1996;Orozco-Montes et al, 2021;Sergievskaya et al, 2021), showing in all the cases that the size of NPs increased with argon pressure. The fact that NPs produced in this work was in a range of 2.4-2.7 nm might be explained by the difference in concentrations of the deposited gold atoms.…”

Sputtering onto liquids: a critical review

“…A wide range of elements has been successfully sputtered onto liquids to create monometallic NPs, including Au [12, 114, 115, 118, 120, 122, 125, 126, 129, 132, 134, 138, 139, 142, 143, 145 -149, 153, 167, 174 -176, 180 -183, 188, 189, 203,204,207,208,210,211,214,216,218,229-238], Ag [11,118,119,123,131,164,175,179,184,185,188,196,205,206, 217, 218, 231-233, 239], Cu [150,155,164,188,189,198,210,230,240,241], Pt [121,133,163,168,169,186,[242][243][244][245], Pd [116,212,231,242,246,247], Fe [11,161,162], In [187], Ni [135] and Mo [20...…”

“…Figure 8: TEM images and corresponding size distributions of Pt NPs produced via MS of a platinum target onto glycerol at pressures of 1, 4, and 9 Pa, respectively.Figure8was reprinted with permission from[163]. Copyright 2021 American Chemical Society.…”