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This application features a method of forming a nanoporous layer. The method includes steps of reducing metal ions in a reverse micelle phase composition to form nanoparticles, removing surfactant from the composition to form clusters of the nanoparticles, dispensing the composition including the na

This application features a method of forming a nanoporous layer. The method includes steps of reducing metal ions in a reverse micelle phase composition to form nanoparticles, removing surfactant from the composition to form clusters of the nanoparticles, dispensing the composition including the nanoparticle clusters dispersed in a liquid on a substrate, and drying to form the nanoporous layer. The nanoporous layer includes nanoparticles deposited to form a three dimensional network of irregularly shaped bodies. The nanoporous layer also includes a three dimensional network of intercluster spaces that are not occupied by the three dimensional network of irregularly shaped bodies.

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1. A method of making a nanoporous layer, the method comprising: providing a liquid composition comprising a surfactant and metal ions, wherein the surfactant is in a reverse micelle phase defining hydrophilic spaces, wherein at least part of the metal ions are kept inside the hydrophilic spaces;add

1. A method of making a nanoporous layer, the method comprising: providing a liquid composition comprising a surfactant and metal ions, wherein the surfactant is in a reverse micelle phase defining hydrophilic spaces, wherein at least part of the metal ions are kept inside the hydrophilic spaces;adding a reducing agent to the liquid composition to cause reduction of at least part of the metal ions to form nanoparticles, which provides a first colloid comprising the nanoparticles dispersed in a first liquid mixture containing the surfactant, wherein at least part of the hydrophilic spaces of the reverse micelle phase is maintained in the first colloid, wherein at least part of the nanoparticles are kept inside at least some of the hydrophilic spaces maintained in the first colloid; andremoving the surfactant from the first colloid to form a second colloid, wherein removing the surfactant causes at least part of the nanoparticles get together and form a number of clusters, wherein the second colloid comprises the clusters dispersed in a second liquid mixture, wherein each cluster has an irregularly shaped body comprising a number of nanoparticles having a generally oval or spherical shape with a length ranging between about 2 nm and about 5 nm,subsequently, adjusting a concentration of the nanoparticles in the second colloid to provide a colloid composition such that the nanoparticles contained in the colloid composition are in an amount between about 0.01 wt % and about 2 wt % with reference to the total weight of the colloid composition;dispensing the colloid composition over a substrate; andsubjecting the dispensed colloid composition to drying to form a nanoporous layer,wherein drying causes the irregularly shaped bodies of the clusters contained in the dispensed composition to deposit over the substrate such that adjacent ones of the irregularly shaped bodies abut one another at some surfaces or portions thereof while forming unoccupied spaces between non-abutting surfaces or portions of the adjacent ones of the irregularly shaped bodies,wherein abutments between adjacent ones of the irregularly shaped bodies connect the adjacent ones with one another, which continues to other ones of the irregularly shaped bodies to form a three-dimensional interconnected network of irregularly shaped bodies,wherein the unoccupied spaces between non-abutting surfaces or portions of the adjacent ones of the irregularly shaped bodies are irregularly shaped and connect with other unoccupied spaces formed by other ones of the irregularly shaped bodies,wherein connections between the unoccupied spaces form a three-dimensional interconnected network of irregularly shaped spaces that is geometrically complementary to and outside the three-dimensional interconnected network of irregularly shaped bodies inside the nanoporous layer,wherein the three-dimensional interconnected network of irregularly shaped bodies comprises numerous nanoparticles that originate from the irregularly shaped bodies of the clusters contained in the colloid composition,wherein, inside the three-dimensional interconnected network of irregularly shaped bodies, adjacent ones of the nanoparticles are apart from each other and form interparticular nanopores without an intervening nanoparticle therebetween,whereby the nanoporous layer comprises the interparticular nanopores inside the three-dimensional interconnected network of irregularly shaped bodies and further comprises the three-dimensional interconnected network of irregularly shaped spaces outside the three-dimensional interconnected network of irregularly shaped bodies,wherein at least part of the interparticular nanopores inside the three-dimensional interconnected network of irregularly shaped bodies are in a size ranging between about 0.5 nm and about 3 nm,wherein at least part of the irregularly shaped spaces of the three-dimensional interconnected network of irregularly shaped spaces are in a size ranging between about 100 nm and about 500 nm. 2. The method of claim 1, wherein, in each cluster, adjacent ones of the nanoparticles are apart from each other and form interparticular gaps therebetween, wherein the clusters comprise a first cluster and a second cluster that are discretely dispersed in the second liquid mixture, wherein each of the first and second clusters has a length ranging between about 50 nm and about 300 nm, wherein the first cluster comprises a first nanoparticle and a second nanoparticle, each of which has a generally oval or spherical shape with a length ranging between about 2 nm and about 5 nm, wherein, inside the first cluster, the first and second nanoparticles are adjacent to each other without an intervening nanoparticle therebetween and apart from each other with an interparticular gap in a size ranging between about 0.5 nm to about 3 nm. 3. The method of claim 2, wherein the second colloid further comprises clusters having a length ranging between 20 and 500 nm. 4. The method of claim 2, wherein the interparticular gaps are distributed generally throughout in each cluster. 5. The method of claim 2, further comprising, subsequent to removing the surfactant, adjusting a concentration of the nanoparticles in the second colloid to provide a colloid composition such that the nanoparticles contained in the colloid composition are in an amount between about 0.01 wt % and about 2 wt % with reference to the total weight of the colloid composition. 6. The method of claim 2, wherein the second colloid further comprises free nanoparticles that are dispersed in the liquid and not bound to a cluster, wherein the free nanoparticles have a generally oval or spherical shape with a length ranging between about 2 nm and about 5 nm. 7. The method of claim 1, wherein no electric potential is applied to the liquid composition for reduction of the metal ion therein. 8. The method of claim 1, wherein the surfactant is a non-ionic surfactant capable of forming an isotropic reverse micelle phase. 9. The method of claim 1, wherein a first one of the clusters comprises a first nanoparticle and a second nanoparticle that are adjacent to each other without an intervening nanoparticle therebetween and apart from each other with a first interparticular gap in a size ranging between about 0.5 nm to about 3 nm. 10. The method of claim 1, wherein removing the surfactant removes a significant amount of the surfactant from the first colloid such that the second colloid is substantially free of the surfactant, wherein if any surfactant is remaining in the second colloid, the surfactant is in an amount smaller than 2 parts by weight with reference to 100 parts by weight of the nanoparticles contained therein. 11. The method of claim 1, wherein the nanoparticles contained in the second colloid are in an amount between about 0.01 wt % and about 2 wt % with reference to the total weight of the second colloid. 12. The method of claim 1, wherein removing the surfactant comprises: centrifuging the first colloid; andcollecting a bottom portion from a centrifuged composition. 13. The method of claim 12, wherein removing the surfactant further comprises: adding a solvent to the collected bottom portion; andrepeating a sequence of centrifuging the solvent added colloid, collecting a bottom portion from its centrifuged composition, and adding the solvent thereto. 14. The method of claim 1, wherein removing the surfactant further comprises adding an acid or base to the first colloid prior to centrifuging, wherein in the first colloid some molecules of the surfactant are bound to nanoparticles, wherein adding the acid or base causes to separate at least part of the molecules of the surfactant from the nanoparticles. 15. The method of claim 1, wherein the nanoparticles contained in the second colloid are in an amount between about 10 wt % and about 40 wt % with reference to the total weight of the second colloid. 16. The method of claim 1, wherein the nanoparticles are primarily made of at least one selected from the group consisting of platinum (Pt), gold (Au), palladium (Pd), rhodium (Rh), titanium (Ti), ruthenium (Ru), tin (Sn), nickel (Ni), copper (Cu), indium (In), thallium (Tl), zirconium (Zr), iridium (Ir), and one or more oxides of the foregoing metals. 17. The method of claim 1, wherein the colloid composition is dispensed in a predetermined amount to form the nanoporous layer having roughness factor between about 100 and about 2500. 18. The method of claim 1, wherein the nanoporous layer is substantially free of a surfactant, wherein if any surfactant is contained in the nanoporous layer, the surfactant is in an amount smaller than 0.5 parts by weight with reference to 100 parts by weight of the nanoparticles contained therein. 19. The method of claim 1, wherein the nanoparticles are primarily made of platinum (Pt) or gold (Au), wherein the interparticular nanopores are distributed generally throughout inside the three-dimensional interconnected network of irregularly shaped bodies. 20. The method of claim 1, wherein the nanoparticles are primarily made of platinum (Pt) or gold (Au), wherein the irregularly shaped spaces of the three-dimensional interconnected network of irregularly shaped spaces are distributed generally throughout in the nanoporous layer. 21. The method of claim 1, wherein at least part of the clusters have a length ranging between about 50 nm and about 300 nm.