Low-dimensional hyperthin FeS

1. An electrode comprising a FeS 2 electrocatalytic material, the FeS 2 electrocatalytic material comprising FeS 2 nanostructures in the form of FeS 2 wires, FeS 2 discs, or both, wherein the FeS 2 wires and the FeS 2 discs are hyperthin having a thickness in the range of from about the thickness of a monolayer of FeS 2 molecules to about 20 nm, and further wherein the FeS 2 nanostructures are polycrystalline comprising a non-pyrite majority crystalline phase.

2. The electrode of claim 1 , wherein the thickness is in the range of from about the thickness of a monolayer of FeS 2 molecules to about 10 nm.

3. The electrode of claim 1 , wherein substantially all the FeS 2 discs have at least partially curved edges.

4. The electrode of claim 3 , wherein substantially all the FeS 2 discs have entirely curved edges.

5. The electrode of claim 3 , wherein the FeS 2 discs comprise circular FeS 2 discs, elliptical FeS 2 discs, or both.

6. The electrode of claim 1 , wherein the non-pyrite majority crystalline phase is marcasite.

7. The electrode of claim 1 , wherein the FeS 2 wires are assembled in the form of bundles, wherein neighboring wires within each bundle are substantially aligned along their lengths and separated by a ligand layer and the FeS 2 discs assembled in the form of stacks, wherein neighboring discs within each stack are substantially aligned along their planes and separated by a ligand layer.

8. The electrode of claim 7 , wherein the bundles or stacks are randomly oriented with respect to one another to define a plurality of pores distributed through the material.

9. An electrode comprising a FeS 2 electrocatalytic material, the FeS 2 electrocatalytic material comprising FeS 2 nanostructures in the form of FeS 2 discs, wherein the FeS 2 discs are hyperthin having a thickness in the range of from about the thickness of a monolayer of FeS 2 molecules to about 20 nm, and further wherein substantially all the FeS 2 discs have at least partially curved edges.

10. The electrode of claim 9 , wherein substantially all the FeS 2 discs have entirely curved edges.

11. An electrochemical system for catalyzing an electrochemical reaction, the system comprising:

(a) an electrochemical cell configured to contain a fluid comprising an electrochemical reactant;

(b) the electrode of claim 1 in contact with the fluid; and

(c) a counter electrode in electrical communication with the electrode of claim 1 .

12. The electrochemical system of claim 11 , further comprising a power source configured to apply an electrical potential across the electrode of claim 1 and the counter electrode in order to generate free electrons for inducing a reduction reaction at the electrode of claim 1 .

13. The electrochemical system of claim 12 , wherein electrochemical reaction is the hydrogen evolution reaction, the fluid is an aqueous electrolyte solution, and the reduction reaction is the generation of H 2 from hydrogen ions and the free electrons.

14. A method for making the electrode of claim 1 , the method comprising:

(a) injecting a first precursor solution comprising sulfur (S), the first precursor solution having a first temperature, into a second precursor comprising iron (Fe), the second precursor solution having a second temperature, to form a reaction mixture, and

(b) allowing the reaction mixture to react at a reaction temperature for a reaction time,

wherein a ratio of Fe:S in the first and second precursor solutions is selected to achieve the nanostructures in the form of FeS 2 wires, FeS 2 discs, or both, wherein the FeS 2 wires and the FeS 2 discs are hyperthin having the thickness in the range of from about the thickness of a monolayer of FeS 2 molecules to about 20 nm, and further wherein the FeS 2 wires and the FeS 2 discs are polycrystalline comprising the non-pyrite majority crystalline phase.

15. The method of claim 14 , wherein substantially all the nanostructures are in the form of FeS 2 discs and the ratio of Fe:S in the first and second precursor solutions is in the range of from about 1:24 to about 1:38.

16. A method of using the electrode of claim 1 to catalyze an electrochemical reaction, the method comprising exposing the FeS 2 electrocatalytic material to a fluid comprising an electrochemical reactant under conditions sufficient to induce the reduction of the electrochemical reactant at the FeS 2 electrocatalytic material-fluid interface to form a reduction product or under conditions sufficient to induce the oxidation of the electrochemical reactant at the FeS 2 electrocatalytic material-fluid interface to form an oxidation product.

17. The method of claim 16 , wherein the electrochemical reaction is the hydrogen evolution reaction, the fluid is an aqueous electrolyte solution, the electrochemical reactant comprises hydrogen ions which are induced to form hydrogen gas as the reduction product in the presence of free electrons.

18. The method of claim 17 , wherein the electrochemical reaction occurs at about neutral pH.

19. The method of claim 17 , wherein substantially all the nanostructures are in the form of FeS 2 discs.

20. The method of claim 19 , wherein the method is characterized by an overpotential of no more than about 90 mV as determined at 0.1 mA/cm 2 in a 0.1 M phosphate buffer at a pH of 7 and a scan rate of 1 mV/s.