Preparing in situ electrocatalytic films in solid polymer electrolyte membranes, composite microelectrode structures produced thereby and chloralkali process utilizing the same

A process for producing a thin, in situ metallic electrocatalytic film proximate the surface of a solid polymer electrolyte membrane to form a composite structure useful in promoting chemical reactions in fuel cells, sensors, chloralkali processes, dialysis, or electrochemical synthesis cells, said method comprising the steps of:

• impregnating a solid polymer electrolyte membrane by ion-exchange with a cationic salt of a selected electrode metal to produce a metal-cation-loaded membrane with a loading level of metal cations sufficient for forming an electronically coherent film of metal particles in electrical contact with one another within the membrane;
• exposing at least one face of the metal-cation-loaded membrane to a chemical reductant to cause the cations in the membrane to diffuse toward the exposed face and to reduce the cations to the metal (0) state while within the membrane, and to produce within the ionomer matrix of the membrane an electronically coherent porous electrocatalytic film of metal predominately within the membrane and near its surface;
• and
• controlling the thickness and morphology of the electrocatalytic film and the electrochemical activity of the resultant composite structure by controlling the loading-level in the impregnating step, and by controlling the temperature, chemical nature and concentration of the reductant.

A chloralkali process of the type wherein respective anode and cathode reaction zones are separated by a solid polymer electrolyte membrane, said process comprising the steps of:

• providing a cathode reaction zone suitable for conducting a gas phase reaction therein;
• providing an anode reaction zone suitable for conducting a liquid phase reaction therein;
• providing, in the space between the anode and cathode reaction zones, a bi-polar structure comprising a solid polymer electrolyte membrane with a thin, porous, electronically conductive, high-surface-area metallic electrocatalytic film of metal particles formed in situ within the ionomer matrix at each surface thereof, where the particles are in electrical contact with one another;
• connecting the films of the bi-polar structure to a power supply so that one film serves as the anode and one film serves as the cathode;
• introducing acidified brine into the anode reaction zone;
• introducing an oxygen containing gas into the cathode reaction zone;
• conducting the following half cell reaction at the anode:
• 4Cl.sup.- .fwdarw.2CL.sub.2 +4e.sup.- ;
• conducting the following half cell reaction at the cathode:
• 0.sub.2 +4H.sup.+ +4e.sup.- .fwdarw.2H.sub.2 O;
• utilizing the high surface area of contact between the ionomer matrix of the solid polymer electrolyte and the electrodes to facilitate the reactions;
• removing chlorine gas and spent brine from the anode reaction zone;
• and
• removing H.sub.2 O plus any excess gas from the cathode reaction zone.

A process for producing an in situ metallic electrocatalytic film proximate the surface of a solid polymer electrolyte membrane to form a composite structure useful in promoting electrochemical reactions in fuel cells, sensors, chloralkali processes, dialysis, electrochemical synthesis cells, said method comprising the steps of:

• impregnating a solid polymer electrolyte membrane with metal ions to produce a metal-ion-loaded membrane, said metal ions being selected as those which will constitute the chemical composition of the electrocatalytic film;
• controlling the loading of the metal ions in the impregnating step to provide a loading of metal ions sufficient for forming an electronically coherent film of metal within the ionomer matrix;
• and
• exposing at least one face of the metal-ion-loaded membrane to a chemical reductant to cause the metal ions in the membrane to diffuse towards the exposed face and to reduce the ions to the metal (0) state while within the membrane and to form in situ within the ionomer matrix of the membrane of the solid polymer electrolyte membrane an electrocatalytic porous film located predominately within the membrane and near its surface having a morphology characterized by metal particles that provide a large surface-area-per-unit volume and which are in electrical contact with each other.