## 2 Experimental
### Electrochemical Setup  
The electrochemical system for the simultaneous EO treatment and hydrogen production is shown in Figure 1, which was custom-made of transparent organic glass. This setup was composed of two sub-cells (each with a 500 mL volume) that were separated by an ion membrane (Sx-2301 DH, Zhongren Int. Co. Ltd. Shanghai, China), which allowed hydrogen ions to pass through. The distance between the anode and the cathode was 20 mm. The HABDD electrode was used as the anode, and a foam nickel (FNi, Dekun Electronic Co. Ltd. Shenzhen, China) electrode was used as the cathode. The electrochemical experiment was carried out under magnetic stirring conditions for electrolytes and mechanical stirring conditions for HABDD. In the electrochemical process, the HABDD was rotated at 100 rpm against the magnetic stirring direction, forming a strong flowing convection of the electrolyte ions. The anodic cell had a water inlet and a gas outlet, as did the cathodic cell. The wastewater samples from the polluted zones were used as the electrolytes in the anodic cell, which was circulated for the EO treatment from an outside water tank by a pump. The circulation flowing rate could be controlled at 20-300 mL/min.  
0.5 M H\({}_{2}\)SO\({}_{4}\) aqueous solution was used as the cathodic electrolyte for performance testing. Water was periodically supplied into the cathodic sub-cell through a valve during the electrolysis process. A custom-made electric source (Gaohu Co. Ltd. Suzhou, China) was used as the power supply. After each circulation, the ion membrane was replaced with a new one. The hydrogen yielding was quantified by drainage of solution in a glass-scaled tube connected to the cathodic cell. The COD values from the anodic cell were monitored at the scheduled time in the EO process [1]. The waste removal efficiency was measured using a UV-Vis spectrometer (UV-3600, Shimadzu, Japan). The UV peaks were the superimposed responses of the various species present in the complex wastewater matrix. All electrochemical experiments were performed in batch mode at room temperature.  
The current efficiency for wastewater mineralization \(E_{\mathrm{w}}\) is calculated by:  
\[E_{\mathrm{w}}=F\cdot V\cdot\Delta COD/(8\cdot I\cdot\Delta t) \tag{1}\]  
where \(F\) is the Faradaic constant (96,485 C/mol), \(V\) is the wastewater volume, \(I\) is the applied current, and \(\Delta COD\) is the change of COD value in the treatment time (\(\Delta t\)). The current efficiency of \(E_{\mathrm{w}}\) for wastewater degradation depended on the electrocatalytic activity of the HABDD electrode, which was evaluated by the COD removal efficiency. The hydrogen production efficiency (\(E_{\mathrm{h}}\)) was determined by electronic hoarding, which was indicated by the ratio of real production to theoretical production.  
The \(E_{\mathrm{h}}\) value is calculated by:  
\[E_{\mathrm{h}}=m/(I\cdot t\cdot m_{0}/F) \tag{2}\]  
where \(m\) is the practical hydrogen production, \(I\) is the current, \(t\) is the time, \(m_{0}\) is the hydrogen production from 1 mol of electron, and \(F\) is the Faraday constant. The decrease in the COD values was referenced as the organic removal efficiency.  
Figure 1: Schematic illustration of the electrochemical system consisting of the rotating HABDD anode and the FNi cathode. The EO process takes place on the HABDD anode. The hydrogen ions generated from the HABDD surface diffuse to the FNi cathode through the ion membrane to form hydrogen gas.