## 3 Results
### Surface Morphology and Elemental Analysis  
Figure 2 displays SEM images of pristine and decorated biochar samples. Figure 2a depicts the surface morphology of CuNi-decorated biochar. It shows a porous, extending surface area for the nanocatalyst-decorated biochar. CuNi nanoparticles are spread along the top of the carbonaceous sample. Upon magnifying the SEM image to provide more comprehensive information, a clearer distribution of the metallic nanoparticles can be observed, as shown in Figure 2b. It is advantageous to notice CuNi nanoparticles covering the inner surface of the pores of biochar in the form of light spots on the inner denser surface surrounded by a circle and ellipse in Figure 2b. CuNi nanoparticles appear as distinct spheres, avoiding any aggregates that may arise in such cases, as illustrated in the inset of Figure 2c. They provide a spherical, undeformed structure for the provided nanoparticles. Upon comparing the B@CuNi surface to that of the pristine biochar, fewer pores can be visualized on the surface, as displayed in Figure 2d. These pores evidently manifest at higher magnification, as illustrated in Figure 2e, in a smaller proportion when compared to the CuNi-biochar sample. The inset in Figure 2f is mentioned here as a reference sample in the absence of the CuNi-supporting catalyst. The bare biochar micrograph denotes a plain surface without much informative morphology, and its porous structure cannot be easily recognized.  
Figure 2: SEM images of biochar/CuNi hybrid (**a–c**) and the reference pristine biochar (**d–f**) without any supported nanocatalysts, at indicated magnifications. Some pores (in (**b**)) enriched with CuNi nanoparticles are surrounded by a circle and an ellipse.  
EDX was used to determine the surface composition of B@CuNi over several spots. For comparison, we have also recorded EDX spectra for OP impregnated with metal salts, and the bare OPs. Figure 3a-c display the EDX spectra of the OPs, OP@metal salts and B@CuNi. The elemental composition of B@CuNi is displayed in Figure 3d, whereas the atomic ratios of (Cu+Ni)/(C+O) and Cu/Ni are compared in Figure 3e for OP@metal salts and B@CuNi. Figure 3a-c conclusively demonstrate the absence of any copper and nickel ions from the surface of the OPs, whereas the characteristic Cu and Ni peaks are noted on the impregnated OP particles with peak intensity increasing in the order Cu-Ni < O < C. The increase in the O/C peak intensity ratio is due to the hydrated metal nitrates. Upon pyrolysis, the metal nitrate-impregnated OPs are transformed into metallic alloy-decorated biochar B@CuNi with relative peak intensity increasing in the order O < Cu-Ni < C. Quantitatively, Figure 3d displays the C, O, Cu and Ni atomic % at 15 spots from the B@CuNi powder sample; the composition is fairly similar from one spot to another, which indicates even decoration of the biochar with metallic nanoparticles. This is due to homogenous impregnation of the OPs with metal nitrates. The (Cu+Ni)/(C+O) atomic ratio (Figure 3d) increases continuously from OP@metal salts to B@CuNi due to the pyrolysis of the olive stones and subsequent release of water and nitrates. Figure 3e shows that the Cu/Ni atomic ratio remains the same within the standard deviation for OP@metal salts (1.00 \(\pm\) 0.10) and B@CuNi (1.125 \(\pm\) 0.277). The Cu/Ni ratio obtained for B@CuNi accounts for the equimolar impregnation of olive pits by metal ions.  
Figure 3: _Cont._