Nanofibrous electrocatalysts
A nanofibrous catalyst and method of manufacture. A precursor solution of a transition metal based material is formed into a plurality of interconnected nanofibers by electro-spinning the precursor solution with the nanofibers converted to a catalytically active material by a heat treatment. Selected subsequent treatments can enhance catalytic activity.
1. A method of preparing a conductive nanofibrous catalyst, comprising the steps of:
preparing a catalytic transition metal precursor solution for making nanofiber containing suspended therein metal organic frameworks and a first nano-fiber forming polymer, an n-containing organic ligand, and a solvent, and the catalyst transition metal precursor solution having a transition metal based active ingredient;
forming a plurality of nanofibers from the precursor solution;
converting the nanofibers to a conductive catalytically active carbonaceous form by applying a thermal curing step comprising heating to less than 300° C. and applying a thermal converting step by heating to between 600° C. and 1100° C. forming a plurality pores throughout the nanofibers with catalytic sites embedded in pores within the nanofibers; and
treating the conductive catalytically active nanofibers to further enhance the catalytic activity.
2. The method as defined in claim 1 further including the precursor solution having a second pore forming polymer.
3. The method as defined in claim 1 , wherein the steps of forming a plurality of nanofibers comprises using an electrospinning method and further wherein first nano-fiber forming polymer is converted in to a graphitic form.
4. The method as defined in claim 1 , wherein the step of converting the nanofibers comprises heat treating the nanofibers and the step of treating the catalytically active nanofibers comprises further chemical treatment.
5. The method as defined in claim 1 , wherein the transition metal active ingredient is dissolved in the precursor solution and is selected from the group of iron porphyrin, cobalt porphyrin, iron phathlocynine, cobalt phathalocine, ferrocene, cobaltacene, 1,10-phenanthroline iron(II) perchlorate, iron acetate, cobalt acetate, manganese acetate, iron nitrate, manganese nitrate, cobalt nitrate, iron chloride, cobalt chloride, and manganese chloride.
6. The method as defined in claim 1 , wherein the metal organic frameworks selected from the group of zeolitic imidazole frameworks consisting of: iron zoelitic imidazole framework (Fe-Im), cobalt zoelitic imidazole framework (Co-Im), iron zoelitic methyl-imidazole framework (Fe-mIm), cobalt zoelitic methyl-imidazole framework (Co-mIm), zinc zoelitic imidazole framework (Zn-Im), zinc zoelitic methyl-imidazole framework (Zn-mlm), and zinc zoelitic ethyl-imidazole framework (Zn-eIm).
7. The method as defined in claim 1 , wherein the first polymer is a fiber forming polymer which is selected from the group of polyacrylonitrile (PAN), polycarboate (PC), polybenzimidazole (PBI), polyurethanes (PU), Nylon6,6, polyaniline (PANI), and polycaprolactone (PCL).
8. The method as defined in claim 1 , wherein the N-containing ligand which is selected from the group of bi-pyridine, aniline, porphyrin, phathlocynine, and phenanthroline.
9. The method as defined in claim 1 , wherein the solvent is selected from the group of dimethyl formamide (DMF), dimethylamine (DMA), N-Methyl-2-pyrrolidone (NMP), methylene chloride, methanol, ethanol, propanol, and acetone.
10. The method as defined in claim 4 , wherein the heat treating step is performed at a time and temperature which produces cross-linking between polymers followed by carbonization of the nanofiber.
11. The method as defined in claim 10 , wherein the temperature of treatment is about 600° C. to 1050° C. and time of treatment is about 20 minutes to 3 hours.
12. The method as defined in claim 1 , wherein the step of treating to enhance catalytic activity comprises acid washing.
13. The method as defined in claim 12 further including the step of treating the acid washed nanofibrous catalyst by re-applying a nitrogen-containing ligand and transition metal organometallic compounds followed by another heat treatment in N-containing gas or inert gas.
14. The method as defined in claim 13 further including the steps of treating the acid washing nanofibrous catalyst by heat treatment in an inert gas atmosphere.
15. The method of claim 1 , wherein the conductive catalytically active carbonaceous form of nanofibers have micro-, meso- and macropores.