Matibag, Via Kryshl Ranillo, et al. “Platinum-Free Electrocatalyst for Oxygen Reduction Reaction Derived from the Direct Pyrolysis of Waste Watermelon Peels”. International Journal of Integrated Engineering, vol. 11, no. 7, Nov. 2019, pp. 175-81, https://publisher.uthm.edu.my/ojs/index.php/ijie/article/view/4639.