Nexion 300q

Soil physicochemical parameters, including temperature, moisture, and electrical conductivity were measured on site with a handheld Thermometer (DT-847U; OneTemp Pty Ltd, Adelaide, SA, Australia) and a HydroSense II Soil Moisture Measurement System (Campbell Scientific Pty Ltd, Garbutt, QND, Australia). Soil pH was determined in deionized water by a pH/EC meter (900-P; TPS Pty Ltd, Brisbane, QND, Australia). Element composition of the soils was analyzed by inductively coupled plasma mass spectrometry (ICP-MS) (Nexion 300Q; Perkin Elmer, Waltham, MA, USA) at LabWest Mineral Analysis Pty Ltd. in Perth, Australia. Detection limits for all elements were at the ng g⁻¹ level. Gold concentrations in soil samples were determined by the aqua regia method^{23 (link)}. Briefly, soil samples were ground to 200 μm, mixed with 100% aqua regia (HCl:HNO₃ = 3:1), and digested at room temperature for 24 h. The supernatant obtained by centrifugation was analyzed by ICP-MS. Total carbon and nitrogen were analyzed by CSBP Lab (CSBP Fertilizers, Kwinana, WA, Australia) using the Dumas high temperature combustion method^{50 (link)}.

TEM images were taken using a Hitachi HT7700 microscope operated at 120 kV by drop casting the nanoparticle dispersions on carbon-coated Cu grids and drying under ambient conditions. High-angle annular dark-field imaging were performed on an aberration-corrected FEI TitanS 80–300 TEM/STEM operated at 300 kV, with a probe convergence angle of 30 mrad and a large inner collection angle of 65 mrad, and a JEOL JEM 2200FS STEM/TEM microscope equipped with a CEOS probe corrector (Heidelberg, Germany) to provide a nominal image resolution of 0.07 nm. The heating experiments were carried out on the FEI microscope using a Protochips Aduro heating stage. To minimize beam irradiation to the sample, a low beam current of 30 pA was used for imaging during heating. The energy-dispersive X-ray spectroscopy analyses were performed in STEM mode using an aberration-corrected JEOL 2200FS electron microscope equipped with a Bruker-AXS silicon drift detector (SDD) detector. The metal contents were measured using ICP-MS (NexION 300Q, PerkinElmer).

S-CoO NRs were fabricated directly on CFP using the cation exchange methodology in the gas phase^{43 (link)}. In this work, CoO NRs were fabricated on both sides of CFP, and the loading of the as-synthesized S-CoO NRs was ~ 0.48 mg cm⁻². The synthetic procedure of S-CoO NRs on a carbon nanotube film and stainless-steel mesh (Supplementary Fig. 10) is the same as on CFP. P-CoO NRs were grown on CFP using a hydrothermal method as detailed elsewhere^{62 (link)}. The loading of P-CoO NRs on CFP was ~ 0.46 mg cm⁻². A commercial 20 wt% Pt/C catalyst (purchased from the Fuel Cell Store), was dispersed in ethanol for at least 30 min with sonication to obtain a homogeneous ink, and ~0.4 mg of Pt/C was loaded per 1 cm² of CFP. The loading of S-CoO NRs, P-CoO NRs, and Pt/C was determined using inductively coupled plasma mass spectrometry (ICP-MS, Perkin-Elmer, NexION 300Q).

Transmission electron microscopy (TEM)
analysis was conducted using a Hitachi HT7700 (Tokyo, Japan) operated
at 120 kV. High-resolution high-angle annular dark-field scanning
transmission electron microscopy (HAADF-STEM) and tomography images
were taken on a JEOL JEM 2200FS STEM/TEM microscope equipped with
a CEOS probe corrector (Heidelberg, Germany) to provide a nominal
image resolution of 0.07 nm. Energy dispersive X-ray (EDX) analysis
was performed in STEM mode using an aberration-corrected JEOL 2200FS
electron microscope equipped with a Bruker-AXS SDD detector. The metal
contents were determined using an inductively coupled plasma mass
spectrometer (ICP-MS, NexION 300Q, PerkinElmer). UV–vis-NIR
extinction spectra were recorded on a Lambda 750 spectrometer (PerkinElmer).