Green Preparation Of Metal Phosphate-based Catalysts Derived From Microorganisms And Their Electrocatalytic Properties For Hydrogen Evolution Reactions

Microbial cells possess abundant surface sites and charges,can provide multiple nucleation centers to interact with metal ions,and control the nucleation and growth of inorganic structures,which are often used as effective templates in the preparation of nanomaterials.However,reports on microbial synthesis are basically related to the preparation of heteroatom-doped biochar catalysts or to carbon carriers,while reports on biosynthesis of metal compounds are extremely rare.In addition,transition metal phosphides are a class of highly efficient hydrogen evolution reactions（HER）electrocatalysis,which plays a non-negligible role in mitigating severe energy conversion crisis.But the preparation of such functional materials usually involves toxic phosphorus source reagents,and releases a large amount of highly flammable and corrosive phosphorus-containing tail gas.In this regard,Saccharomyces that are inexpensive,abundant,and easy to culture are selected as a source of phosphorus to achieve green synthesis of transition metal phosphides and efficient electrocatalytic HER studies.In addition,the reaction mechanism between Saccharomyce cells and metals was proposed,and the active source of catalysts for HER was discussed.（1）Using Saccharomyce cells as a template to adsorb metal cobalt ions and graphene nanosheets as a separating agent to prevent agglomeration,a high activity HER electrocatalyst（Co-Co₂P@NPC/rGO）with multi-stage porous structure was prepared.That is,the Co-Co2P heterogeneous nanoparticles possessing a size of about 104.7 nm supported on the graphene nanosheets are embedded in the the nitrogen\phosphorus double doped porous carbon with hollow structure.Saccharomyce cells provide not only carbon source for the production of carbon shells,but also phosphorus source for the preparation of metal phosphides.In order to improve the practicability,a binderless three-dimensional（3D）electrode composed of powdered Co-Co₂P@NPC/rGO catalysts is further developed,which manifests excellent catalytic activity(low overpotential of 61.5 mV at 10 mA cm^-2)and catalytic stability at high current densities（e.g.1000 mA cm^-22 for 20 h）in 0.5 M H₂SO₄ electrolyte.This work provides a biological template method that can be used to rationally design and prepare metal or metal compound@biocarbon 3D electrodes,which possesses broad application prospects in energy storage and conversion.（2）Aerogel electrocatalyst（Ni-Ni₃P@NPC/rGO）with a 3D graphene network framework was synthesized from the carbon matrix structure of Saccharomyce cells and in situ phosphating of metals.Compared with the use of excessive toxic phosphorus sources to synthesize metal phosphides,in-situ phosphating of metallic nickel with Saccharomyces as phosphorus source is a simple,economical and environmentally friendly phosphating process.In addition,the catalyst exhibited excellent bifunctional catalytic performance for HER(low overpotential of 73 mV at 10 mA cm^-2)and urea degradation reaction(UDR,only 1.38 V up to 50 mA cm^-2).Furthermore,a two-electrode electrolytic cell constructed by a 3D bulk electrode supported by a graphite fiber brush（Ni-Ni₃P@NPC/rGO/GFB）realizes efficient urea-based wastewater electrolysis（HER&UDR）,which saves 448 mV to drive a current density of 500 mA g^-11 compared to water splitting.This work enables the coupling of electrocatalytic high-efficiency hydrogen production and degradation of organic pollutants at lower input voltages.