Transition metal phosphide supported on carbon nanosheets

1. An electrode, comprising an electrically conductive substrate coated with an electrocatalyst, the electrocatalyst comprising:

nanoparticles of an iron phosphide; and

carbon nanosheets as a catalyst support, the carbon nanosheets having no nitrogen or phosphorus doping, and the carbon nanosheets being interconnected with covalent carbon-carbon bonds,

wherein the carbon nanosheets branch by at least partially peeling so that a single nanosheet branches into multiple nanosheets each individually having a continuous structure but covalently connected to one or more core or nucleus nanosheets,

wherein the nanoparticles have an average diameter in the range of from 3 to 30 nm, and the carbon nanosheets have a thickness of no more than 3 nm,

wherein the molar ratio of the nanoparticles of the iron phosphide to the carbon nanosheets is in a range of from 0.15 to 0.3,

wherein the electrode has a BET surface area in a range of from 140 to 200 m 2 /g,

wherein the electrode has a hydrogen evolution reaction turnover frequency in a range of from 0.90 to 0.30 s 1 ,

and wherein the electrode has an overpotential in a hydrogen evolution reaction to produce a current density of 10 mA/cm 2 in acidic conditions in a range of from 50 to 104 mV.

2. The electrode of claim 1 , wherein the nanoparticles are homogenous spherical nanoparticles having a diameter in a range of from 2 to 20 nm.

3. The electrode of claim 1 , wherein the electrocatalyst is present on a surface of the electrode in a range of from 0.2 to 10 mg/cm 2 .

4. The electrode of claim 1 , wherein the BET surface area of the electrode is in the range of from 160 to 180 m 2 /g.

5. The electrode of claim 1 , wherein the electrically conductive substrate is selected from the group consisting of glassy carbon, graphite, gold, platinum, silver, iron, copper, and aluminum.

6. The electrode of claim 1 , wherein the nanoparticles have an average diameter in a range of from greater than 4 to 15 nm.

7. The electrode of claim 1 , wherein the turnover frequency is in a range of from 0.70 to 0.50 s −1 and the overpotential to produce the current density of 10 mA/cm 2 in acidic conditions is in a range of from 100 to 104 mV.

8. The electrode of claim 7 , wherein the electrocatalyst is present on a surface of the electrode in an amount in a range of from 1 to 2 mg/cm 2 , and the iron phosphide is supported on interconnected carbon nanosheets.

9. The electrode of claim 1 , wherein the carbon nanosheets are not doped with any other material.

10. The electrode of claim 1 , wherein interconnections of the carbon nanosheets represent points at which a first carbon nanosheet is at least partially unraveled or opened and suffers a nanosheet structural defect point, and

wherein, at the defect point, carbon or graphene-like material of the carbon nanosheets branches from the first carbon nanosheet to form a second carbon nanosheet.

11. The electrode of claim 1 , wherein the carbon nanosheets consist of carbon.

12. The electrode of claim 1 , wherein the carbon nanosheets consist of graphene.

13. The electrode of claim 1 , wherein the interconnected carbon nanosheets form a dendrimer structure.

14. An electrochemical cell, comprising:

the electrode of claim 1 as a working electrode,

a counter electrode, a reference electrode, and

an electrolyte.

15. The electrochemical cell of claim 14 , wherein the electrolyte is an aqueous alkali metal hydroxide or a mineral acid at a concentration in a range of from 0.1 to 2.0 M.

16. The electrochemical cell of claim 14 , wherein the electrolyte is 0.5 M aqueous sulfuric acid.

17. An electrochemical method for producing hydrogen from water comprises;

contacting the working electrode of the electrochemical cell of claim 14 with water,

applying an electric potential to the working electrode; and

forming hydrogen by electrolytically splitting water.