Hydroxyl radical (•OH) can hydroxylate or dehydrogenate organics without forming extra products, thereby expediently applied in extensive domains. Although it can be efficiently produced through single-electron transfer from transition metal-containing activators to hydrogen peroxide (H2O2), narrow applicable pH range, strict activator/H2O2 ratio requirement, and byproducts that are formed in mixture with the background matrix, necessitate the need for additional energy-intensive up/downstream treatments. Here, we show a green Fenton process in an electrochemical cell, where the electro-generated atomic H* on a Pd/graphite cathode enables the efficient conversion of H2O2 into •OH and subsequent degradation of organic pollutants (80% efficiency). Operando liquid time-of-fight secondary ion mass spectrometry verified that the H2O2 activation takes place through a transition state of the Pd-H*-H2O2 adduct with a low reaction energy barrier of 0.92 eV, whereby the lone electron in atomic H* can readily cleave the peroxide bridge, with •OH and H2O as products (∆Gr=-1.344 eV). Using H + or H2O as the resource, we demonstrate that the welldirected output of H* determines the pH-independent production of •OH for stable conversion of organic contaminants in wider pH ranges (3~12). The research pioneers a novel path for eliminating the restrictions that are historically challenging in traditional Fenton process.

In order to enhance Cu−EDTA decomplexation and copper cathodic recovery via the photoelectrocatalytic (PEC) process, S 2 O 8 2− was introduced into the PEC system with a TiO 2 /Ti photoanode. At a current density of 0.2 mA/cm 2 and initial solution pH of 3.0, the decomplexation ratio of Cu complexes was increased from 47.5% in the PEC process to 98.4% with 5 mM S 2 O 8 2− addition into the PEC process (PEC/S 2 O 8 2− ). Correspondently, recovery percentage of Cu was increased to 98.3% from 47.4% within 60 min. It was observed that nearly no copper recovery occurred within the initial reaction period of 10 min. Combined with the analysis of ESR and electrochemical LSV curves, it was concluded that activation of S 2 O 8 2− into SO 4 ·− radicals by cathodic reduction occurred, which was prior to the reduction of liberated Cu 2+ ions. UV irradiation of S 2 O 8 2− also led to the production of SO 4 ·− . The generated SO 4 ·− radicals enhanced the oxidation of Cu−EDTA. After the consumption of S 2 O 8 2− , the Cu recovery via cathodic reduction proceeded quickly. Acidification induced by the transformation of SO 4 ·− to OH· favored the copper cathodic recovery. The combined PEC/S 2 O 8 2− process was also efficient for the TOC removal from a real electroplating wastewater with the Cu recovery efficiency higher than 80%.