Dual strategies to enhance mineralization efficiency in innovative electrochemical advanced oxidation processes using natural air diffusion electrode: Improving both H2O2 production and utilization efficiency

• Natural air diffusion electrode (NADE) improved H 2 O 2 production without aeration. • Innovative electro-Fenton (EF) and photoelectro-Fenton (PEF) using NADE were developed. • A new H 2 O 2 utilization efficiency (HUE) evaluation index in EF and PEF was proposed. • PEF had a higher HUE than EF but not cost-effective due to higher energy consumption. • Upgrading with EF-PEF maintained high mineralization efficiency and reduced energy consumption. High mineralization efficiency and low energy consumption are the core requirements for the application of electrochemical advanced oxidation processes (EAOPs) for organic pollutants degradation. Herein we reported innovative EAOPs using natural air diffusion electrode (NADE) to improve H 2 O 2 production and enhanced utilization efficiency by combination with electro-Fenton and photoelectro-Fenton (EF-PEF) for the degradation of 2,4-dichlorophenoxyacetic acid. At 0.2 and 1.2 A, the H 2 O 2 production on NADE possessed 158% and 188% of that on normal aeration electrode (AE) with the total energy consumption only 7.2% and 25.4% of that on AE, respectively. Such excellent H 2 O 2 production performance on NADE was attributed to ultra-high oxygen mass transfer efficiency and the feature of not requiring aeration, which reduced energy consumption greatly. A new H 2 O 2 utilization efficiency (HUE) evaluation index including decomposition ratio, conversion efficiency and total utilization efficiency of H 2 O 2 was proposed, demonstrating that PEF had a higher HUE than EF but not cost-effective due to a higher energy consumption. EF-PEF was thus proposed to upgrade the traditional PEF, which reduced energy consumption while maintained high mineralization efficiency. The HUE in EF-PEF process was greatly improved and superior to most reported EAOPs in literatures, which explained the high mineralization efficiency (78%–87%) with an extremely low energy consumption (0.065–0.167 kWh (g TOC) −1 ) even an order of magnitude lower than that in the literatures. This work enlightened the importance of two strategies of improving both H 2 O 2 production and utilization efficiency to maintain high mineralization efficiency in H 2 O 2 based EAOPs.