Surface modifications with heteropoly and isopoly oxometalates: Part I. Qualitative aspects of the activation of electrode surfaces towards the hydrogen evolution reaction

Abstract

It is shown that heteropoly and isopoly oxometalates and even tungstic acid can be used to modify the surfaces of materials as diverse as gold, tungsten, mercury, glassy carbon, graphite and even platinum. Except for platinum, all these electronic conductors are usually very poor surfaces on which to evolve hydrogen. Upon modification, they all appear to exhibit strikingly high exchange current densities with respect to the hydrogen evolution reaction (h.e.r.). The Keggin structure or the Dawson structure of the starting compound does not induce any specific characteristic for the modified electrode, nor does the very nature of the electrode material. In particular, mercury has been successfully derivatized. It has been ascertained by various surface analysis techniques, that the observed enhancement of catalytic activity of the chemically derivatized electrodes is not caused by traces of noble metal impurities which could accumulate during the modification process and explain the phenomena. It has also been shown that a possible increase of the microscopic surface area upon modification cannot solely and primarily account for the several orders of magnitude increase measured for the exchange current density for the h.e.r. The activation is durable and the catalyst seems perfectly suitable for use in non-purposely purified solutions. A judicious selection of the starting compounds is made to demonstrate that oxometalates of the tungstic, molybdic and the mixed (W, Mo) series can be used.