## 3 Results and Discussion
### Anperometric Response to Hydrogen Peroxide  
Figure 7A shows the amperometric responses of Pt/rGOP towards H\({}_{2}\)O\({}_{2}\) at different applied potentials (0.0 to \(-\)0.3 V). The result reveals that Pt/rGOP exhibits the highest current density once the applied potential was \(-\)0.25 V. Figure 7B depicts the amperometric response changes with the different electrodeposition cycles. The current density gradually increased, with the electrodeposition cycles increased from 5 to 20, and further to 25, and the current density substantially reduced. This is because PtNPs exhibit an agglomerating phenomenon, comparing with the specimen deposited for 20 cycles. The result demonstrates that electrodeposition for 20 cycles in rGOP could obtain the largest electroactive area. The amperometric response of Pt/rGOP to successive additions of different concentrations of H\({}_{2}\)O\({}_{2}\) in 0.1 mol/L PBS with potential applied at \(-\)0.25 V is given in Figure 7C. It shows the sensor has a fast response and the current is able to reach a dynamic equilibrium within 5 s after adding H\({}_{2}\)O\({}_{2}\). The fast response indicates a favorable electron transfer between Pt/rGOP and H\({}_{2}\)O\({}_{2}\). It is found that the amperometric responses towards H\({}_{2}\)O\({}_{2}\) concentration is wide, from 0.2 umol/L to 8.5 mmol/L, and the detection ranges are divided into two linear sections: 0.2 umol/L to 2.0 mmol/L and 2.0 to 8.5 mmol/L, while the sensitivities are 67.51 \(\mu\)A cm\({}^{-2}\) mM\({}^{-1}\) and 40.21 \(\mu\)A cm\({}^{-2}\) mM\({}^{-1}\), respectively,  
Figure 6: CV curves of (**A**) Pt foil, rGOP and Pt/rGOP in deaerated 0.5 mol/L H\({}_{2}\)SO\({}_{4}\) with a scan rate of 50 mV/s, and (**B**) Pt foil and Pt/rGOP in 0.1 mol/L PBS containing 1.0 mmol/L H\({}_{2}\)O\({}_{2}\) saturated with nitrogen gas. (**C**) Nyquist plots of Pt/rGOP, rGOP electrodes in deaerated 0.1 mol/L KCl, containing 1.0 mmol/L K3 Fe(CN)\({}_{6}\) and 1.0 mmol/L K4 Fe(CN)\({}_{6}\). Frequency range: 0.1–10\({}^{5}\) Hz. as shown in Figure 7D. The existence of two linear ranges could indicate different mechanisms: at low concentrations of hydrogen peroxide, the electrocatalytic mechanism is dominant. Otherwise, at high concentration of hydrogen peroxide, the direct reduction of hydrogen peroxide on the surface can play an important role in the analytical signal [45]. Moreover, the detection limit of H\({}_{2}\)O\({}_{2}\) can be as low as 100 nmol/L, at a signal-to-noise (S/N) ratio of 3. The sensor provides a more comparable detection limit and linear range compared to previous reports, as listed in Table 1. In the meantime, Pt/rGOP exhibits the highest sensitivity among all the sensors. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Electrode** & \begin{tabular}{c} **Sensitivity** \\ **(\(\mu\)A cm\({}^{-2}\) mmol\({}^{-1}\))** \\ \end{tabular} & \
\begin{tabular}{c} **LOD** \\ **(\(\mu\)mol/L)** \\ \end{tabular} &
\begin{tabular}{c} **Liner Range** \\ **(\(\mu\)mol/L)** \\ \end{tabular} & **Ref.** \\ \hline Au@PB NPs graphene paper & 5.0 & 0.1 & 1–30 & [46] \\ AuNPs/graphene paper & 0.24 & 2 & 5–8600 & [47] \\ PtNPs/graphene film & 0.56 & 0.2 & 0–2500 & [48] \\ PtNPs/MnO\({}_{2}\) nanowires/graphene paper & 0.13 & 1 & 2.0–13.3 & [49] \\ HRP/graphene paper & 0.56 & 1.7 & 3.5–329 & [50] \\ AgNCs/graphene film & 0.18 & 3.0 & 20–10,000 & [51] \\ AuNPs-Porous graphene film & 0.08 & 0.1 & 0.5–4900 & [52] \\ PtNPs/graphene paper & 67.51 & 0.1 & 0.2–2000 & This work \\ PtNPs/graphene paper & 40.21 & & 2000–8500 & This work \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparison of various graphene-based electrodes for H\({}_{2}\)O\({}_{2}\) sensing. Figure 7: **(A)** Histograms of the current responses of Pt/rGOP electrode to 0.2 mmol/L H\({}_{2}\)O\({}_{2}\) in PBS at a different applied potential.