Abstract
The hydrogen economy presents an appealing energy future but its implementation must solve numerous problems ranging from low-cost sustainable production, high-density storage, costly infrastructure, to eliminating safety concern. The use of renewable carbohydrate as a high-density hydrogen carrier and energy source for hydrogen production is possible due to emerging cell-free synthetic biology technology—cell-free synthetic pathway biotransformation (SyPaB). Assembly of numerous enzymes and co-enzymes in vitro can create complicated set of biological reactions or pathways that microorganisms or catalysts cannot complete, for example, C6H10O5 (aq) + 7 H2O (l) à 12 H2 (g) + 6 CO2 (g) (PLoS One 2007, 2:e456). Thanks to 100% selectivity of enzymes, modest reaction conditions, and high-purity of generated hydrogen, carbohydrate is a promising hydrogen carrier for end users. Gravimetric density of carbohydrate is 14.8 H2 mass% if water can be recycled from proton exchange membrane fuel cells or 8.33% H2 mass% without water recycling. Renewable carbohydrate can be isolated from plant biomass or would be produced from a combination of solar electricity/hydrogen and carbon dioxide fixation mediated by high-efficiency artificial photosynthesis mediated by SyPaB. The construction of this carbon-neutral carbohydrate economy would address numerous sustainability challenges, such as electricity and hydrogen storage, CO2 fixation and long-term storage, water conservation, transportation fuel production, plus feed and food production.
Highlights
The hydrogen economy is a hypothetical future energy system, where hydrogen will be used as an energy storage carrier for end users, especially in the transport sector
Two of the major advantages of the hydrogen economy are (i) much higher energy conversion efficiency from chemical energy to electricity through fuel cells compared to internal combustion engines, whose maximum efficiencies are restricted by the Second Law of thermodynamics, and (ii) nearly no pollutants generated at the sites of end users [2,3]
We presented a new concept—the carbon-neutral carbohydrate economy based on the use of renewable carbohydrate as a high energy density hydrogen carrier (Figure 1a), discussed great potential of the carbohydrate economy, and highlighted future
Summary
The hydrogen economy is a hypothetical future energy system, where hydrogen will be used as an energy storage carrier for end users, especially in the transport sector. At the point of end users, hydrogen gas can be generated from their decomposition or reaction with water In addition to their low hydrogen densities, cost-effective regeneration of hydride or light metals must be addressed. 7.5% reversible H2 mass at conditions between −40 to +85 °C and between 1.5 to 150 bars of H2 pressure and 70 kg of total releasable hydrogen/m3 [3] Another alternative to address the hydrogen storage challenges is use of high energy density hydrogen carriers, such as hydrocarbon, biodiesel, methanol, ethanol, ammonia and carbohydrate [3,13,14,15].
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