Economical electrolyser solution

Abstract

In the market there are conventional alkaline electrolysers and advanced polymer membrane electrolysers, with higher performance, but they are both quite expensive. Indeed, the materials commonly utilized for water electrolysis in alkaline electrolysers are those based on Raney nickel and their alloys, but these materials are expensive. Taking into account those aspects, the following work aims, as other authors [Olivares-Ramíreza JM, Campos-Corneliob ML, Uribe Godínezb J, Borja-Arcob E, Castellanosb RH. Studies on the hydrogen evolution reaction on different stainless steels. Int J Hydrogen Energy 2007; 32: 3170–3. [1]; Henrique dos Santos Andrade M, Lima Aciolia M, Ginaldo da Silva Juniora J, Carlos Pereira Silvaa J, Oliveira Vilarc E, Tonholoa J, Preliminary investigation of some commercial alloys for hydrogen evolution in alkaline water electrolysis. Int J Hydrogen Energy 2004;29:235–41. [2]], to highlight how it is possible to produce hydrogen in economical ways using less advanced technologies. A conventional alkaline electrolytic cell, “lab-electrolyser”, has been built using economical material. It is composed of electrodes of 5.0 cm×5.0 cm characterized by a current density of about 250 mA/cm² and an efficiency of about 65% at 55 °C; the cell produces about 2.7 Nl/h of hydrogen. The overall cost of this devise has been compared with the cost of the electrolysers available on the market, hypothesizing a linear dependence cost with the productive capacity. The conclusion has been that there is a big margin for costs decreasing even taking into account all the auxiliary systems for an electrolysis process.

Introduction

Hydrogen is the fuel for the future, and the future is “today”. The hydrogen economy is still at the beginning but the society, innovation, and market push inexorably towards hydrogen, inspiring the idea of an energy integrated system that can satisfy, in an independent way, the energy needs of small-sized consumers. According to the “closed cycles philosophy” [3], [4] of our research group (GEA—Energy and Environment Group—of CIRPS—Interuniversity Center of Research For Sustainable Development, University of Rome “La Sapienza”), the integrated system should perform a closed cycle—ecologically neuter and sustainable because using renewable resources generates power without producing refusals [5]. To size energetically the system the average energy needs of an Italian family for 1 day has been taken into account. The assessment is about 9 kW h and 55% of this energy is supposed to be used during the daily hours directly from the photovoltaic system. The remaining energy to be supplied is 4 kW h during the evening and the night. Therefore, this amount of energy has to be produced and stored during the day exploiting the sunshine or wind energy. How can this be done? This can be achieved by producing hydrogen from water and accumulating it either in a normal tank or in a special one containing a particular material able to adsorb and desorb hydrogen. To produce hydrogen, an electrolyser that splits distilled water into hydrogen and oxygen has been taken into account. The main unit is the electrolysis stack where the electric energy from the photovoltaic or eolic system is converted into chemical energy producing hydrogen [6]. This hydrogen has to be stored and the two main options under consideration are a conventional cylinder tank or a special one inside which a particular material adsorbs and desorbs hydrogen [5]. There are several kinds of materials capable of receiving and releasing hydrogen due to their own crystalline structure, which hosts the hydrogen atoms. All of the current methods and the projected technologies of producing hydrogen from solar energy are much more costly (greater than a factor of 3) when compared with hydrogen production from coal or natural gas plants. This high difference puts enormous pressure on the need of reducing the cost of a solar energy recovery device. Nowadays all system components are very expensive as well as the electrolyser. In the future, as the cost of the fuel cell approaches $50/kW, the cost of an electrolytic cell to electrolyse water is also expected to approach a low number (about $125/kW).