Cubic Phase Templating of Mesoporous Platinum – Synthesis, Characterisation & Electrocatalytic Properties.

Abstract

The synthesis and application of mesoporous platinum materials with novel 3D cubic morphology and large pore spacing by utilising two amphiphilic molecules Brij® 58 and F127 as structure-directing agents was explored. Brij® 58 and F127, when mixed with water or hexacholorplatinic acid (HCPA), were found to form stable mesophases such as the face centred cubic (FCC), body centred cubic (BCC), hexagonal (HI ), and lamellar (L∝), according to small angle x-ray scattering (SAXS) and cross polarising light microscopy (CPLM) data. This versatility made these systems ideal for mesoporous platinum synthesis. Interestingly, mesoporous platinum nanoparticles, ranging from 23 to 57 nm, were fabricated through a polyol synthesis-like mechanism at 80 °C utilising Brij® 58/HCPA at concentrations ranging from 30 to 60 wt% with no additional reducing agent. Mesoporous platinum electrodes (MPEs) were created using FCC (40 wt% of Brij® 58 ) and BCC templates (30 wt% of Brij® 58 and 50 wt% of F127). The FCC template from Brij® 58/HCPA was employed to create MPEs at various potentials. The electrodes exhibited interesting surface features and an internal 3D cubic morphology most likely to be a diamond structure with pore diameters varying from 3.0 to 3.5 nm and lattice parameters ranging from 6.3 to 7.1 nm. They also demonstrated high electrochemically active surface areas (ECSA) with values up to ~27.6 m2 g −1 and improved catalytic activity towards ethanol in acidic media. They illustrated high JF/JB ratios reaching a maximum of 1.19 and low onset potentials (Eonset) reaching a minimum of 0.35 V. Electrochemical impedance spectroscopy (EIS) emphasised small charge transfer resistance (Rct) and large double layer capacitance (Cdl) values for the MPEs. All films also demonstrated good long-term stability. The BCC template of Brij® 58/HCPA was utilised to fabricate the MPEs at different potentials. The electrodes revealed exciting surface morphology and an internal 3D cubic morphology most likely to be a primitive structure with pore diameters ranging from 3.0 to 3.5 nm, and lattice parameters between 6.4 and 6.8 nm. Films revealed high ECSA reaching up to a maximum of ~ 31.2 m2 g -1 for thin films and all films exhibited excellent catalytic activity towards ethanol oxidation. They demonstrated high JF/JB ratios reaching a maximum of 1.38 and low Eonset values reaching a minimum of 0.33 V. All films also exhibited excellent long-term stability. The BCC template of F127/HCPA was used for electrodeposition of MPEs at various potentials. These MPEs revealed an internal 3D cubic morphology most likely to be a primitive structure with large pore diameters of between 7.8 and 8.2 nm and lattice parameters from 16.4 to 17.4 nm. Electrodes presented high ECSA ranging up to ~ 24.5 m2 g -1 and superior catalytic activity for ethanol oxidation as recognised by high JF/JB ratios increasing to a maximum of 1.05 and low Eonset values with a minimum of 0.37 V. EIS analysis highlighted good efficiency for ethanol oxidation, represented by low values of Rct and large Cdl values. The electrodes also displayed good long-term stability. All MPEs in this study demonstrated, high ECSA and excellent catalytic activity for ethanol oxidation as evidenced by high JF/JB ratios, low Eonset values and enhanced stability. This behaviour, coupled with the interesting external surface morphology and internal cubic mesoporosity, suggests the potential for further applications (batteries, capacitors and other types of electrocatalysis) of these materials.