Microbial Reducing Bacteria Assisted Synthesis Of Two Heteroatom-Dopped Cobalt Hydroxides For Electrocatalytic Oxygen Evolution Reaction

In order to cope with the looming energy and environmental crisis,it is urgent to develop a green and sustainable new energy system.Oxygen evolution reaction（OER）has been widely studied as an important component in energy conversion technologies,such as water splitting,reversible zinc-air batteries,and carbon dioxide reduction.OER involves four electron transfer processes,and its reaction kinetics are slow.Currently,iridium and ruthenium-based catalysts are still needed to reduce the reaction barrier.However,their high cost and scarce reserves severely limit the large-scale application of these precious metal catalysts.Therefore,it is urgent to develop cheap,highly active and stable OER catalysts.In recent years,hydroxides have shown excellent electrocatalytic performance in OER and demonstrated the potential to replace precious metal-based catalysts.In order to further improve the performance of the catalyst,non-metallic heteroatoms doping shows significant efficacy in optimizing the electronic band structure of the catalyst in terms of catalyst design and performance optimization.At present,the doping of heteroatomic sulfur elements usually requires high temperature and high pressure conditions,accompanied by the production of a large amount of toxic gases and waste liquids that pollute the environment.However,some anaerobic microbes can reduce different valence states of S into S^2-and combine them with metals,which are safe and environmentally friendly.Therefore,in this paper,two kinds of modified cobalt hydroxide catalysts were prepared by the bacterial vulcanization method,which is friendly to environment,low cost and easy to scale production.The main content of the paper is divided into two parts:（1）Microbial vulcanization modified cobalt hydroxide nanosheets and its OER performanceWe synthesized sulfur-modified cobalt hydroxide nanosheets using Shewanella oneidensis MR-1,named MV-S/Co（OH）2.MV-S/Co（OH）2 was loaded with uniform Co4S3nanoparticles with an average particle size of 6.3 nm.MV-S/Co（OH）2 showed excellent OER performance in 1 M KOH,with an overpotential of 289.4±2.0 m V at the current density of10 m A·cm^-2,which was 75 m V higher than that of Co（OH）2.At the same time,MV-S/Co（OH）2 also exhibits excellent electrochemical stability,maintaining 98.5%of its OER performance after electrolysis for 32 hours at a current density of 100 m A·cm^-2.（2）Study on inorganic-organic double doping cobalt hydroxide nanosheets derived from microbial sulfide MOF and their OER propertiesWe prepared inorganic-organic dual-doped cobalt hydroxide nanosheets,named MV-S/Co（OH）2/MI,by sulfidating ZIF-67 with Shewanella oneidensis MR-1 bacteria to introduce both inorganic sulfur（S）and organic dimethyl imidazole（MI）ligands.The specific surface area of MV-S/Co（OH）2/MI is 117 m²·g^-1.The inorganic-organic dual doping improves the valence state of the active center Co,making MV-S/Co（OH）2/MI shows excellent electrocatalytic OER performance that can reach the current density of 10 m A·cm^-2 with only 252.8±2.0 m V in 1 M KOH.The current density decreased by only 3%after electrolyzed for over 200 hours at a current density of 100 m A·cm^-2.Moreover,the overall water-splitting device assembled with MV-S/Co（OH）2/MI as the anode and Pt/C as the cathode only needs 1.47 V to drive the current density of 10 m A·cm^-2.