Nanostructured electrodes for hydrogen production in alkaline electrolyzer

Abstract

Ever-widespread employment of renewable energy sources, such as wind and sun, request the simultaneous use of effective energy storage systems owing to the intermittent and unpredictable energy generation by these sources. The most reliable storage systems currently under investigation are batteries and electrochemical cells for hydrogen production from water splitting. Both systems store chemical energy which can be converted on demand. The low power density is the weakness of the batteries while the high production cost limits currently the wide use of hydrogen from electrochemical water splitting. In this work, attention was focused on the use of nanostructured Ni as a cathode for electrochemical production of hydrogen from alkaline solution. The work is aimed at analysing the energy dissipation at 0.5 Acm−2, which is a value of applicative interest, for detecting one of the cause determining the high production cost. The development of electrochemical cells employing alkaline solution is currently the most promising approach in comparison with electrolysers using acidic solution which are expensive, because require precious metals as electrodes and high cost cation-selective membrane for efficiently conducting water splitting. Nanostructured Ni electrodes were fabricated through a cheap and easily scalable process, based on the Ni electrodeposition inside the pores of a commercial polycarbonate membrane acting as a template. On the contrary, a galvanic connection driving a spontaneous displacement reaction was employed for synthesising Pd nanostructured electrode which was tested for comparison purposes. Once the membrane is dissolved in an organic solution, the electrodes were initially characterized by SEM, EDS and XRD analysis. Then, electrochemical tests were performed to evaluate electrocatalytic properties of the electrodes. The tests were conducted through either cyclic or linear sweep voltammetry in 30% w/w KOH aqueous solution. Then, the nanostructured electrodes were tested under constant current density of 0.5 Acm−2. In comparison with nanostructured Pd, Ni electrodes with the same morphology and in otherwise identical conditions show a better response in terms of electrocatalytic activity. In addition, these electrodes showed satisfying stability over time through tests longer than 60 h. The analysis of energy dissipation revealed that the prevalent contribution was due to the ohmic drop)which can be reduced through a properly cell design) based on the accurate control of the parameters determining ohmic drop inside the cell.