H2O2 is a major transmitter of redox signals in electrochemical processes, whose detection is relevant for various industries. Herein, we developed a new fabrication method for a Cu2O/Cu nanowire-based nonenzymatic H2O2 electrochemical sensor that was decorated with irregular TiO2-x nanoparticles deriving form Ti3C2 MXene. The TiO2-x/Cu2O/Cu-NW electrodes possess excellent selectivity, stability, and reproducibility for H2O2 detection in both EC and PEC operational modes. In the EC detection of H2O2, the TiO2-x/Cu2O/Cu-NW electrode shows a linear relationship in the range from 10 μM to 42.19 mM and a low detection limit of 0.79 μM (S/N = 3), which has a similar sensitivity but a much broader linear range compared with the commercial H2O2 analyzer (0-5.88 mM, Q45H/84, US-QContums). It also shows excellent recovery in detecting H2O2 in the real orange juice and milk samples with the recovery ranging from 96.9 to 105%, indicating the potential for practical applications. In the PEC detection of H2O2, the TiO2-x/Cu2O/Cu-NW electrode shows a lower detection limit of 59 nM (S/N = 3), which is 13 times more sensitive than the EC electrode. The enhanced PEC performance can be attributed to the formation of p-n heterojunction between TiO2-x and Cu2O, which improves light utilization and inhibits the recombination of photo-induced electrons and holes. This work illuminates the extraordinary potential of MXene-derived TiO2 in electrochemical and photoelectrochemical applications.