Electrochemical Synthesis Of Hydrogen Peroxide By Co-based Non-noble Metal Catalyst In Acidic Medium

Hydrogen peroxide（H₂O₂）,as an important chemical product,plays an important role in medical disinfection,paper bleaching,chemical industry,sewage treatment and so on because of its green and environmental advantages.The industrial production of H₂O₂ predominately relies on energy-intensive anthraquinone process,which suffers from transportation risk,complicated operation and serious secondary pollution.Recently,electrochemical synthesis of H₂O₂ using a 2e^-oxygen reduction reaction（2e^-ORR）has been recognized as a promising alternative to anthraquinone processes.The main challenge to the process is to develop high activity,selectivity and stability of 2e^-ORR catalysts with industry-related productivity.At present,the best performance is still based on noble metals and their alloys.However,its commercial adoption is hampered by high costs,which are urgently needed to reduce in order to increase market penetration.Based on this,the aim of this paper is to develop 2e^-ORR cobalt-based catalysts with low cost,high performance and long life.The main works are summaried below:（1）Here,in order to improve the stability of Co-based catalyst in acidic medium,the traditional Co/C catalyst,Co-NPs anchored by rich-defect carbon black,was used as the research object to find an effective method.Based on the concept of strong metal-support interaction（SMSI）,we investigated the effect of anchoring between different support（such as C-S,Ce O₂,Al₂O₃）and Co-NPs on the electrocatalytic stability.Unfortunately,the durability has improved too little for further application.Therefore,the Co/C catalyst was further modified to form a composite Co/C-GPO with paraffin oil and graphite ball milling,which created a local hydrophobic environment on the catalyst surface to relieve the dissolution rate.In the cyclic voltammetry（CV）stability test,the electrochemical activity of Co/C-GPO was almost not lost after 1,500 cycles,and the overpotential was the same as the original value,which confirmed the feasibility of local hydrophobic protection strategy to improve the stability,and provided a new path for optimizing the stability of cobalt-based catalyst.（2）Another challenge of Co-based catalysts is that the selectivity is potential dependent and the catalytic range is narrow.Therefore,we propose to engineer the coordination environment of metal compounds to achieve the regulation of ORR pathway.Herein,Co₉S₈/C catalyst was synthesized at different temperatures to investigate the effects of isolated sites and ligand environment on the catalytic activity and selectivity of 2e^-ORR.Co₉S₈/C-800℃reveal E_onset of 0.72 V vs.RHE,indicating that the 2e^-ORR pathway was successfully realized at the Co site isolated by the S atom.However,the adjacent Co-Co spacing is difficult to inhibit O-O bond dissociation,which is easy to activate H₂O₂ and further reduce to H₂O,resulting in a H₂O₂selectivity of only 30%.The above confirmed that isolated sites and ligand effects are critical in regulating the ORR pathway.Moreover,the phenomenon of poor selectivity still needs to be further optimized.（3）Herein,we further optimized the structure and composition of cobalt compounds to solve the previous problem of H₂O₂ selectivity.Therefore,cobalt phosphoselenide（Co PSe/C）was constructed for the efficient electrochemical synthesis of H₂O₂.Combined DFT calculations show that the free energy of Co PSe is optimized by the synergistic effect of P and Se to be closer to the ideal state of 0 e V,and that the binding energy of Co sites for OOH*is similarly tuned.Therefore,Co PSe/C reveals an onset potential of 0.68 V vs.RHE in the 0.1 M HCl O₄,and maintained a high selectivity of up to 85%in a wide potential range of 0-0.5V to overcome the potential dependence challenge.Moreover,in the stability test of the H-type electrolytic cell,the yield of 0.45 m M H₂O₂ solution accumulated was 87 mmol g_cat^-1 h^-1 after continuous electrolysis for 10 h.Finally,Co PSe/C catalyst achieves efficient degradation of Rhodamine B and phenol in electrofenton wastewater treatment system,due to superior electrocatalytic performance of H₂O₂ production.