context: (4) PEC: a typical PEC process (Fig. 9D) could be regarded as a combination of electrocatalysis, photocatalysis and their synergistic effects from mechanism. On one hand, electrocatalysis could generate functional radicals (e.g. ˙OH) to degrade oxidizable contaminants at the anode and reduce others at the cathode. On the other hand, the photocatalysis subprocess excites e−/h+ to degrade the existing pollutants. In particular, the electrons generated by photocatalysis could migrate along the electric field to the counter electrode by the utilized positive potential (Fig. 9D), which contributes to the reduction of photo-generated holes' and electrons' recombination and thus enhancement of photocatalytic performance. In other words, the increase of bias potential would not only enhance the separation of excitons but also elevate the degree of the electrochemical reaction, which would contribute to the acceleration of PEC performance.