Short communicationClean hydrogen production from methanol–water solutions via power-saved electrolytic reforming process
Highlights
► Clean hydrogen production by electrochemical reforming of methanol–water solutions. ► Pt could be the more effective electrocatalysts in comparison with PtRu. ► Methanol electrolysis can save more than 65% electrical energy.
Introduction
As hydrogen release via water electrolysis promises to be of great future importance, scientific efforts are oriented to the improvement of the electrolytic process efficiency. The most commonly used commercial water electrolyzers are based on the alkaline or proton exchange membrane (PEM) technology. The cost of hydrogen produced in this manner is largely determined by the cost of electrical energy expended. The energy requirement to produce hydrogen by the water electrolysis is in turn governed by the operating voltage, a quantity determined by the thermodynamic potential for water electrolysis and the efficiency of the process. For water electrolysis, the operating voltage is typically over 1.4 V even in the most efficient electrolyzer [1], [2], [3]. If this operating voltage is lowered, the energy requirements can be reduced dramatically and correspondingly the cost of hydrogen production.
From this standpoint, the replacement of water at the anode side with organic molecules can be used to produce clean H2 which can be utilized in other systems, resulting in an improvement in the overall system performance. Such an electrochemical reforming or electrolysis has been demonstrated using several different sources [4], [5], [6], [7], [8], [9], [10]. Botte et al. have reported that the electrooxidation of aqueous ammonia on PtIr catalysts in alkaline electrolyzer allows for the production of high purity hydrogen at cell voltages as low as 0.36 V [4], [5]. Recently several studies including a patent by Narayanan et al. have focused on H2 production by electrolysis of methanol–water solutions [6], [7], [8]. They have dealt with various parameters to be considered for methanol electrolysis. In fact, the standard potential for the methanol oxidation is only −0.016 V (vs. SHE) compared to 1.23 V for the water oxidation. It has been estimated that H2 production from methanol electrolysis costs about 50% less compared to that of water, even when the cost of methanol is taken into account [6].
In this paper, we report results obtained for methanol electrolysis to optimize the operating conditions with respect to current efficiency, methanol loss, and which is more effective electrocatalyst. Also, the energy consumption of methanol electrolysis are evaluated and compared with that of water electrolysis under given conditions.
Section snippets
Experimental
The chemicals used in this study were PtRu and Pt black (Johnson Matthey), isopropyl alcohol and methanol (Junsei), 5% Nafion solution (1100EW, DuPont) and Millipore water (18.2 MΩ). The catalyst inks were prepared by dispersing the catalyst nanoparticles into appropriate amounts of water, 5% Nafion ionomer solution and isopropyl alcohol. Pt black (3 mg cm−2) and PtRu black were used as anode catalysts, and Pt black (3 mg cm−2) was used as cathode catalyst, respectively. Then both the anode and
Results and discussion
A set of experiments were carried out to study of effects of cell temperature and methanol concentration on the methanol electrolysis. It can be seen in Fig. 2 that current density increases with cell temperature. This is as expected, since both methanol oxidation kinetics and hydrogen production rate improve as cell temperature increases. Current efficiency, however, decreases with an increase of cell temperature as shown in Fig. 2(d). This is due largely to the mechanism of methanol
Conclusions
Operating conditions of the electrolytic hydrogen production by electrochemical reforming of methanol–water solutions are optimized in terms of current efficiency and catalysts stability, and energy requirements were compared with conventional water electrolysis. Current efficiency increases with current density, while decreasing with cell temperature. While PtRu has been known to be best electrocatalyst for methanol oxidation in direct methanol fuel cells, Pt could be the more effective
Acknowledgment
This work is supported by a grant from the Industrial Source Technology Development Programs (10033093) of the Ministry of Knowledge Economy (MKE), South Korea.
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