# Heterogeneous Electro-Fenton-like Designs for the Disposal of 2-Phenylphenol from Water
## 2 Materials and Methods
### Heterogeneous Nickel Electrocatalyst  
Nowadays, a challenge of the modern electro-Fenton systems is to improve the characteristics of the cathodes to enhance hydrogen peroxide production. In this sense, several authors have focused their studies on the evaluation of several cathode modification strategies that can improve its properties and increase electric conductivity [57; 58]. Among the wide range of approaches reported for the enhancement of the production, cathodes synthesised by merging carbonaceous materials and Teflon (polytetrafluoroethylene or PTFE) have achieved interesting results [59; 60]. In addition, to improve the electro-Fenton process, the inclusion of metals in the cathode can act as a heterogeneous catalyst with the capacity to react with electrogenerated hydrogen peroxide [31; 61; 62]. In this context, the inclusion of nanofibers doped with nickel has been tested to perform the heterogeneous electro-Fenton process. Due to a large number of experiments need to evaluate the effect of cathode composition, in this study, a Taguchi design was used to reduce the number of trials required to obtain a valid conclusion [63]. Taguchi uses orthogonal matrices, which organise the variables that affect the process and their levels, in the most likely to affect the process. In addition, it offers the opportunity to reduce the number of experiments by testing pairs of combinations, saving time and resources. It allows the calculation of a signal-to-noise ratio (S/N) based on experimental data, which defines the best experimental conditions, considering product quality or process performance within the range of process performance within the experimental range tested. In this study, the cathodes were prepared by immersion of carbon felt in a dispersion solution of ethanol:ultrapure water that contained carbon black, nickel nanofibers and PTFE (Figure 5). In this study, the Taguchi method was used to investigate the effect of three operating parameters to obtain an optimal process within the evaluated range. The selected variables were A: carbon black, B: nickel nanofibers and C: PTFE and the used concentrations were summarised in Table 2.  
The current intensity was also tested since depending on the composition, the response of the prepared electrodes could be different about carbon felt cathode. Thus, the Taguchi method to ascertain the significance of each of the factors chosen in the hydrogen peroxide production was evaluated operating at 100 and 300 mA. The effect of the input variables on the hydrogen peroxide has been determined by the S/N ratio with the larger-the-better criteria and the attained response values were therefore converted into S/N. As an example, Figure 6 shows the main effect plots for the response at intensity current of 100 mA. Thus, the strongest influence is the nickel nanofibers, followed by carbon black and PTFE. Moreover, the main effect plots determine the optimum factor levels. As can be seen, A\({}_{2}\)B\({}_{2}\)C\({}_{1}\) are the optimal condition operating at both current intensities. These improvements of hydrogen peroxide could be attributed to the change in the surface cathode with, for example, the formation of microporous by deposition of carbon black and nanofibers. In Figure 7, the profiles of produced hydrogen peroxide and 2-phenylphenol removal operating with the optimized cathode at 100 and 300 mA are shown. Figure 5: Detailed SEM image of an electrocatalyst containing carbon black, nanofibers, PTFE and nickel (**a**,**b**) and EDS analysis: fluorine (**c**) and nickel (**d**). Figure 6: Main effects plot for S/N ratios with the larger-the better criteria of screening experiment yield. Responses of hydrogen peroxide produced at 100 mA. (A: carbon black, B: nickel loaded nanofibers and C: PFTE content). Figure 7: Profiles of hydrogen peroxide (**a**) and 2-phenylphenol removal (**b**) using the optimized electrocatalys in electron-Fenton-like process at 100 mA (marron) and 300 mA (orange) and current efficiency evolution along time (**c**).