Urea as a hydrogen carrier: a perspective on its potential for safe, sustainable and long-term energy supply

Abstract

Recently, there have been publications reporting the use of urea, as a source of hydrogen/fuel cell power. There have however been no reports that singularly assess the suitability of urea for this purpose. This article provides not only a perspective on the attributes of urea ((NH 2 ) 2 CO) as a hydrogen carrier for fuel cells but also presents the findings of a review on the feasibility of utilising the enormous natural resource of urea that exists. Urea is a cheap and widely available commodity with well developed manufacturing infrastructure and a rapidly increasing volume of production. This offers rapid implementation of urea for application as a hydrogen carrie r either directly or as a source of ammonia. Compared with other industrial chemicals previously considered, urea has the advantages of being non-toxic, stable, and therefore easy to transport and store. This report reveals that the natural resource of urea could be a solution to long-term future sustainable hydrogen supply and that the present status of scientific knowledge necessary to extract this natural resource is in the most part understood. It is considered realistic that these sustainable routes could be exploited if they are given sufficient focus of research attention.

Electrocatalytic oxidation of urea on a sintered Ni–Pt electrode

“…(NiOOH to Ni(OH) 2 ). During potential scanning in an alkaline solution, nickel can be oxidized to Ni(OH) 2 , which can occur in two crystallographic phases (i.e., a-Ni(OH) 2 and b-Ni(OH) 2 ) [15,16]. During scanning, a-Ni(OH) 2 forms first, and this phase is converted to the more stable bNi(OH) 2 with increasing time and potential.…”

“…. In the voltammograms of the solution with added urea, the anodic oxidation of Ni(OH) 2 to NiOOH and the oxidation of urea overlapped. In the electrochemical measurements (i.e., cyclic voltammetry and chronoamperometry), the sintered Ni-Pt electrode exhibited higher activity than the Ni and Ti/Pt electrodes and was successfully employed for the electrocatalytic oxidation of urea.…”

“…However, the oxidation peak for the conversion of Ni(OH) 2 to NiOOH was less visible (Fig. 2b) due to the overlap of the anodic oxidation of Ni(OH) 2 to NiOOH and the oxidation of urea. At higher scan rates, the small reduction peak for the conversion of c-NiOOH to bNi(OH) 2 was also visible.…”

“…As one of the main end products of metabolism in most animals, urea is present in large quantities in the environment [1]. Another source of urea is wastewater generated during the production of urea [2,3]. Wastewater containing urea can be purified by various methods.…”

Urea removal from aqueous solutions—a review

“…Urea electrolysis is catalyzed by the trivalent nickel ions in NiOOH, which is the reason why the total cell voltage in a electrolytic cell operating according to reactions (1-2) and (9) is equal to 0.37 V which is notably less than 1.23 V, which is a requirement for commencing the water splitting reaction. So far, there have been only a few reviews and theoretical deliberations published concerning urea as a potential hydrogen and energy carrier [61,62]. In these papers, it is argued that urea is much more convenient to store and transport than hydrogen; however, there is a need for the on-site conversion of urea to hydrogen, and the use of an electro-catalytic process at nickel-based anodes seems to be a very promising alternative for this purpose.…”