Hydrogen evolution on nickel incorporated in three-dimensional conducting polymer layers

The paper discusses results on the development of nickel/conducting polymer composite layers used as catalysts in the hydrogen evolution reaction (HER). Conducting polymers (CP), polypyrrole (PPY), and polyaniline (PANI) are used as three-dimensional pattering templates (matrices) for electrodeposition of nickel on an inert glassy carbon surface. It is shown that Ni/CP layers offer a significantly higher overall electrocatalytic activity in the HER than Ni electrodeposited on a flat two-dimensional substrate. This is a result of favorable Ni/CP morphology which yields an increase in the active surface area of the catalyst. The overall best catalyst is a Ni/PANI layer formed by incorporation of small amounts of Ni into a thick pre-deposited PANI layer. The resulting porous layer is composed of ca. 3 mu m interconnected spherical Ni particles, with an almost complete surface absence of PANI. The increased porosity of the layer is of a great benefit at high HER overpotentials, where accumulation of produced molecular hydrogen inside the catalyst layer is prevented. Due to a lower porosity, all the Ni/PPY catalytic layers studied are susceptible to the surface blockage (hydrogen accumulation) at high overpotentials. However, in the lower overpotential region, a Ni/PPY catalyst formed by incorporating a larger amount of Ni into a. thin porous pre-deposited PPY layer offers an electrocatalytic HER activity comparable to the best Ni/PANI catalyst. When PPY and Ni are electrodeposited simultaneously (co-deposition method), a substantial decrease in a diameter of Ni islands, down to 100 nm, and an increase in the island surface density are obtained. (c) 2005 Elsevier B.V. All rights reserved.