Method for modifying electrocatalyst material, electrochemical cells and electrodes containing this modified material, and synthesis methods utilizing the cells

Claim 3

An electrocatalyst with modified electrochemical characteristics which has been prepared according to the method of claim 1.

Claim 4

An electrocatalyst according to claim 2, wherein about 30 to about 75% of the transition metal atoms at the exposed surface of said electrocatalyst are bound to a reduced form of the oxidized sulfur-containing species.

Claim 5

An electrochemical cell comprising a cathode, an anode, and an electrolyte in contact with the cathode, and the same or a different electrolyte in contact with the anode, wherein a surface of the anode or the cathode comprises an electrocatalyst of claim 2.

Claim 6

An electrochemical cell according to claim 4, wherein a surface of the anode comprises said electrocatalyst.

Claim 7

An electrochemical cell according to claim 4, wherein a surface of the cathode comprises said electrocatalyst.

Claim 8

An electrochemical cell according to claim 4, wherein said anode and said cathode each comprise two major surfaces, one major surface of the cathode being a reaction-catalyzing surface suitable for contact with a reducible reactant; one major surface of the anode being a reaction-catalyzing surface suitable for contact with an oxidizable reactant; the said electrocatalyst being present at one or both of the said reaction-catalyzing surfaces.

Claim 9

A method for partially and selectively reducing or oxidizing a starting material in the electrochemical cell of claim 4, comprising the step of bringing said starting material into contact with said electrocatalyst and carrying out an electrochemical oxidation or reduction.

Claim 10

A method according to claim 8, wherein the starting material is elemental oxygen or a gaseous or water soluble oxide which is electrochemically selectively reduced to a particular lower oxidation state.

Claim 11

A method according to claim 9 in which nitric oxide is selectively reduced to hydroxylamine, with only minor amounts of nitrogen, nitrous oxide, or ammonia formed as by-products.

Claim 12

A method according to claim 8, wherein the starting material is an organic compound which is electrochemically and selectively oxidized to a higher oxidation state less than +4.

Claim 13

A method according to claim 8 which is carried out electrogeneratively, with recovery of the electrical energy produced by said cell.

Claim 14

An electrochemical synthesis electrode comprising the electrocatalyst of claim 2 and a current collecting means in operative electrical contact with said electrocatalyst.

Claim 15

A method according to claim 1, comprising the steps of: (a) contacting an exposed surface of an electrocatalyst material, containing a transition metal of the second or third triad of Group VIII of the Periodic Table, with sulfur dioxide until the sulfur dioxide has become bound to said transition metal, at least to about 15 to about 100 atomic % of said transition metal in said exposed surface of said electrocatalyst material, by means of at least two types of bonding: a wash-resistant bond, whereby the thus-bound sulfur dioxide is not substantially removed by washing or leaching with a neutral or acidic oxygen-containing aqueous medium; a relatively weaker bond, as compared to said wash-resistant bond, whereby the thus-bound sulfur dioxide can be substantially removed by washing or leaching with a neutral or acidic oxygen-containing aqueous medium which substantially does not affect sulfur dioxide bound to said transition metal by the wash-resistant bond; (b) washing the thus-treated exposed surface of said electrocatalyst material with a neutral or acidic oxygen-containing aqueous medium containing dissolved oxygen to decrease the said atomic % of transition metal bound to sulfur dioxide in said exposed surface by at least about 5 atomic % so that no more than 95 atomic % of said transition metal in said exposed surface is bound to sulfur dioxide, but at least 10 atomic % of said transition metal in said exposed surface is bound to sulfur dioxide; (c) after steps (a) and (b) have been completed, chemically or electrochemically reducing the sulfur dioxide still bound to still transition metal to obtain an electrocatalytic surface of increased selectivity comprising electrocatalytic transition metal sites 10-95% occupied by the reduced sulfur dioxide.

Claim 16

A method according to claim 14, comprising the steps of: (a) contacting said exposed surface with sulfur dioxide, in the presence of an acidic aqueous medium, until about 40 to about 100% of the electrocatalytically active sites in the said exposed surface have been occupied by sulfur dioxide bound to said transition metal at said surface, in part by the wash-resistant bond and in part by the relatively weaker bond; (b) removing sulfur dioxide bound to the said transition metal at said surface by said relatively weaker bond, said removal being carried out by means of a soak with a solution of sulfuric acid containing dissolved oxygen which is essentially free of sulfur dioxide, said soak having substantially no effect upon said sulfur dioxide bound to said transition metal at said surface by said wash-resistant bond; (c) removing said sulfuric acid solution from said exposed surface, in order to recover a surface-treated electrocatalyst material having >10% but no more than about 75% of its surface electrocatalytic sites occupied by sulfur dioxide stil bound to said transition metal at said surface by said wash-resistant bond; (d) after said steps (a) through (c) have been completed, electrochemically reducing said sulfur dioxide still bound to said transition metal at said surface by said washresistant bond; said electrochemical reduction being carried out in an electric cell, electrogeneratively at an E cell of 0-0.9 volt, or electrolytically by applying a voltage of up to about 0.9 volt to said cell; and (e) recovering an electrocatalyst material in which >10% but <75% of the surface transition metal catalytic sites thereof are substantially permanently modified by a reduced sulfur dioxide which is not removed by use of the electrocatalyst in a cell electrode at imposed or electrogeneratively produced cell voltages of up to about 0.9 volt.

Claim 17

A method according to claim 1 wherein the oxidized sulfur-containing species is electrochemically reduced to sulfur or sulfide.

Claim 18

A method according to claim 1 wherein said decreasing step is carried out by washing or leaching the exposed surface of the electrocatalyst material with an aqueous medium which is substantially free of any oxidized sulfur-containing species having a sulfur oxidation state less than +6.

Claim 19

A method according to claim 1, wherein the amount of oxidized sulfur-containing species bound to said transition metal at said exposed surface is decreased to less than about 75 but >10 atomic % of the said transition metal at said exposed surface.

Claim 20

A method according to claim 1, wherein said decreasing step is carried out by non-electrochemical means in the presence of air.

Claim 21

A method according to claim 19, wherein said decreasing step is carried out by washing in the presence of dissolved air.

Claim 22

A method according to claim 1, wherein the electrocatalyst material comprises particles of a transition metal in an activated state or a carrier or support material provided with surface transition metal in an activated state.

Claim 23

A method according to claim 21, wherein the particles of transition metal in an activated state comprise platinum black.

Claim 24

A method according to claim 21 wherein the electrocatalyst material further comprises a hydrophobic polymer.

Claim 25

An electrocatalyst with modified electrochemical characteristics which has been prepared according to the method of claim 21.

Claim 26

An electrocatalyst according to claim 2, wherein the electrocatalyst has been treated with a hydrophobic polymer.

Claim 27

An electrochemical cell according to claim 4, wherein said electrocatalyst has been treated with a hydrophobic polymer.

Claim 28

An electrochemical synthesis electrode according to claim 13, wherein the electrocatalyst has been treated with a hydrophobic polymer.

Claim 29

A method according to claim 8, wherein the electrocatalyst has been treated with a hydrophobic polymer.

Claim 30

A method for electrogeneratively reducing nitric oxide substantially selectively to hydroxylamine in an electrogenerative cell comprising a cathode, an anode, and an electrolyte in contact with an electrocatalytic surface of the cathode, the same or a different electrolyte being in contact with a surface of the anode, the surface of said cathode opposite to said electrocatalytic surface of the cathode being gas-permeable, said method comprising: bringing a gas comprising nitric oxide into contact with the gas-permeable surface of said cathode and hence by permeation into contact with the electrocatalytic surface of the cathode, said electrocatalytic surface comprising an electrocatalytic material modifed in accordance with the method of claim 1 or claim 2, operating said cell electrogeneratively at an E cell voltage of about 0 to 0.9 volt, and recovering the resulting hydroxylamine.

Claim 33

A method according to claim 30, wherein said decreasing step is carried out by soaking with a solution containing dissolved air.

Claim 34

A method according to claim 31, wherein the particles of transition metal in an activated state comprise platinum black.

Claim 35

A method according to claim 31 wherein the electrocatalyst material further comprises a hydrophobic polymer.