Nonprecious metal catalyst for hydrogen production from neutral solutions
Catalysts comprising MoP and MoP 2 are disclosed, wherein the catalyst is a composite. The catalyst may have a molar ratio of MoP:MoP 2 within a range of 5:95 to 95:5. The catalyst may be used as a cathode active material for hydrogen generation from neutral pH solutions, such as wastewater or seawater. Methods of making the catalyst also are disclosed.
1. A catalyst, comprising:
regions of crystalline MoP; and
regions of crystalline MoP 2 , the catalyst having a molar ratio of MoP:MoP 2 within a range of 5:95 to 95:5,
wherein the catalyst is a composite of MoP and MoP 2 , and
the regions of crystalline MoP and regions of crystalline MoP 2 have Mo-terminated surfaces.
2. The catalyst of claim 1 , wherein the composite is a nanocomposite comprising nanoparticles having an average largest dimension within a range of 5-50 nm.
3. The catalyst of claim 1 , wherein:
the MoP regions comprise (101) planes and the MoP 2 regions comprise (020) planes.
4. A method of making a catalyst, comprising:
combining (i) M + n [PMo 12 O 40 ] n- where 3≤n≤27 and M is a +1 cation and (ii) MH 2 PO 2 in a M + n [PMo 12 O 40 ] n- /MH 2 PO 2 mass ratio within a range of 1:4 to 1:7 to provide a mixture;
heating the mixture in an inert atmosphere at a first temperature T 1 within a range of 240° C. to 300° C. for a first period of time to form MoP x where 1<x<2; and
subsequently heating the MoP x in the inert atmosphere at a second temperature T 2 within a range of 675° C. to 725° C. for a second period of time to form a catalyst comprising MoP and MoP 2 , the catalyst having a molar ratio of MoP:MoP 2 within a range of 5:95 to 95:5,
wherein the catalyst is a composite of MoP and MoP 2 .
5. The method of claim 4 , wherein the first period of time is at least one hour.
6. The method of claim 4 , wherein the second period of time is at least four hours.
7. The method of claim 4 , wherein the inert atmosphere comprises argon, nitrogen, helium, or any combination thereof.
8. The method of claim 4 , further comprising preparing the M + n [PMo 12 O 40 ] n- by:
preparing an aqueous solution comprising a phosphomolybdate (POM);
adding a reducing agent to the aqueous solution with stirring;
continuing to stir for an effective period of time to reduce POM and form a solution comprising nanoclusters of M + n [PMo 12 O 40 ] n- ; and
drying the solution comprising the nanoclusters to obtain M + n [PMo 12 O 40 ] n- .
9. The method of claim 8 , wherein the reducing agent is NaBH 4 and M + n [PMo 12 O 40 ] n− is Na + n [PMo 12 O 40 ] n- .
10. The method of claim 9 , wherein the effective period of time is at least one hour.
11. The method of claim 8 , further comprising preparing the POM by:
preparing an aqueous solution comprising a molybdate and H 3 PO 4 in a molar ratio≤1:0.58 with stirring;
adding 10-15 mol HNO 3 per mol of the molybdate dropwise to the aqueous solution with stirring;
incubating the aqueous solution at a temperature within a range of from 60° C. to 100° C. for at least two hours, thereby producing a solution comprising POM; and
recovering POM from the solution comprising POM.
12. A product made by the method of claim 4 .
13. The method of claim 4 , wherein M is Na, K, or NH 4 .