1. Diagram of preparation process and chemical mechanisms of Pt_100-xIr_x alloy aerogels

S1. SEM image of Pt₈₀Ir₂₀ aerogel

2. Structure and composition of Pt₈₀Ir₂₀ alloy aerogel

3. (a) XRD patterns of different catalysts, commercial Pt/C, and (b) corresponding enlarged XRD patterns in the range of 2θ=35°-50°

4. (a) XPS survey spectrum of Pt₈₀Ir₂₀ aerogel, (b) Pt4f XPS spectra of various Pt-based catalysts, and (c) Ir4f XPS spectrum of Pt₈₀Ir₂₀ aerogel

S2. TEM images of Pt aerogel

S3. TEM images of Pt₈₀Ir₂₀ alloy

5. (a) CV curves of Pt_100-xIr_x aerogels and commercial Pt/C catalysts under room temperature, (b) AOR activity comparison for Pt_100-xIr_x aerogels and commercial Pt/C catalysts at 0.5 V(vs. RHE), (c) energy difference between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of Pt, Ir and Pt₈₀Ir₂₀ nanoparticles, (d) schematic diagram of electrocatalytic ammonia oxidation of Pt₈₀Ir₂₀ alloy nanoparticles and Pt₈₀Ir₂₀ alloy aerogel, (e) CV curves of the Pt₈₀Ir₂₀ catalyst in the presence and absence of NH₃; (f) CA curves of Pt_100-xIr_x aerogels and commercial Pt/C catalysts

6. Electrochemical active areas of catalysts and AOR performance before and after 2000 CV cycles

S4. EDS spectrum of Pt₈₀Ir₂₀ aerogel catalyst with inset showing its mass and atom ratios

7. (a) CV curves of the Pt₈₀Ir₂₀ aerogel tested in different NH₃ concentrations, (b) AOR activity comparison for Pt₈₀Ir₂₀ aerogel and commercial Pt/C in different NH₃ concentrations at 0.5 V(vs. RHE), and (c, d) CA curves of the Pt₈₀Ir₂₀ aerogel (c) and commercial Pt/C (d) at 0.65 V(vs. RHE)

8. (a-c) CV curves of catalysts at different temperatures, (d) AOR activity comparison for commercial Pt/C, Pt aerogel and Pt₈₀Ir₂₀ aerogel catalysts at different temperatures at 0.5 V(vs. RHE), (e) CA curves of the Pt₈₀Ir₂₀ aerogel at different temperatures at 0.65 V (vs. RHE), (f) Arrhenius plots for NH₃ oxidation on commercial Pt/C, Pt aerogel and Pt₈₀Ir₂₀ aerogel catalysts at 0.5 V(vs. RHE)

S5. Electrochemical active surface area of Pt, Pt₈₀Ir₂₀ aerogels

S6. Nyquist plots of EIS spectra measured for Pt (violet), Pt₈₀Ir₂₀ aerogel (blue) and commercial Pt/C (gray) in 1.0 mol/L KOH electrolyte at the open circuit potential

S7. XRD patterns of Pt₈₀Ir₂₀ aerogel before and after 2000 cycle stability tests

S8. TEM images of Pt₈₀Ir₂₀ aerogel

S9. CV curves of the commercial Pt/C in different NH₃ concentrations

Table 1. Elemental quantification (%, in atom) determined by XPS for different Pt_100-xIr_x aerogel catalysts

Table 2. Comparison of binding energy between Pt4f with different Pt-based catalysts

Table 3. Comparison of AOR activity between different catalysts