Powering the Hydrogen Economy from Waste Heat: A Review of Heat‐to‐Hydrogen Concepts

Abstract

Ever‐increasing energy demands and environmental concerns require new and clean energy supplies, many of which are intermittent and do not correlate with demand. To balance supply with demand, a universal energy vector should be employed such that intermittent renewable energy can be stored and transported and then used when needed. Hydrogen is the perfect universal energy vector and a possible solution that ensures environmental cleanliness, maximum utilization of renewable energy sources, and high efficiency, whereby the combustion of the fuel yields only water. One abundant and freely available energy source—both anthropogenic and natural—is heat. Heat can be obtained from industrial processes and is indeed often viewed as a waste product with a premium to remove but is notoriously difficult to capture, store, and transport. Capturing and storing low‐grade heat therefore provides a significant opportunity and can be achieved by coupling thermoelectric generators and water electrolyzers. A thermoelectric generator is placed within a thermal energy gradient and produces a flow of current that is fed to the electrolysis unit with which it produces hydrogen and oxygen as the final products. The hydrogen can be stored for long periods and transported for “on‐demand” use in fuel cells for electricity from hydrogen burners for a return to thermal energy. This Review summarizes the current state‐of‐the‐art research into implementing thermoelectric generators and utilizing heat as a primary energy source to produce hydrogen, which could replace the need for extra electric power to run hydrogen production units. Furthermore, suitable requirements, modifications, and other related aspects associated with such a new and novel method of hydrogen generation are discussed. Hydrogen produced from otherwise‐wasted energy sources can be considered to be green.

From Renewable Energy to Renewable Fuel: A Sustainable Hydrogen Production

“…alongside, research on coupling STEGs to the electrolysis is also under progress (Baranowski, Snyder et al, 2012). Industrial waste heat is a fantastic source of cheap energy that can be utilized for hydrogen production (Mulla & Dunnill, 2019). Thermoelectric generators work on the principle of Seebeck effect, in which a temperature gradient applied across the device produces useful electric potential.…”

“…The low efficiency of the thermoelectric generators is a major drawback to be used independently in the production of hydrogen, and therefore they can be used as a supplementary source by coupling with photovoltaic to improve overall efficiency or production rate (Mulla & Dunnill, 2019). At present, the commercial thermoelectric generators are mainly contained materials like Bi 2 Te 3 and PbTe which makes them quite expensive, and also the elements like tellurium (Te) are highly toxic and scarce hence, a large-scale implementation facing difficulties (Mulla & Dunnill, 2019;Mulla & Rabinal, 2019). Nevertheless, rigorous scientific investigations are under progress which produced many new, low-cost and non-toxic materials and improvements can be realized in the near future (Mulla & Rabinal, 2018;Mulla & Dunnill, 2019).…”

“…At present, the commercial thermoelectric generators are mainly contained materials like Bi 2 Te 3 and PbTe which makes them quite expensive, and also the elements like tellurium (Te) are highly toxic and scarce hence, a large-scale implementation facing difficulties (Mulla & Dunnill, 2019;Mulla & Rabinal, 2019). Nevertheless, rigorous scientific investigations are under progress which produced many new, low-cost and non-toxic materials and improvements can be realized in the near future (Mulla & Rabinal, 2018;Mulla & Dunnill, 2019). The efficiency argument however does need to be taken in context as the use of otherwise wasted heat yields green value from waste (Mulla & Dunnill, 2019) and is economically viable even with low efficiency, especially if the TEG can be produced cheaply (Mulla & Rabinal, 2018;Mulla, Jones et al, 2020).…”

“…Nevertheless, rigorous scientific investigations are under progress which produced many new, low-cost and non-toxic materials and improvements can be realized in the near future (Mulla & Rabinal, 2018;Mulla & Dunnill, 2019). The efficiency argument however does need to be taken in context as the use of otherwise wasted heat yields green value from waste (Mulla & Dunnill, 2019) and is economically viable even with low efficiency, especially if the TEG can be produced cheaply (Mulla & Rabinal, 2018;Mulla, Jones et al, 2020).…”

“…ProtonExchange Membrane Electrolysis Cells (PEMEC), and (iii) Solid Oxide Electrolysis Cells (SOEC) of which AECs have been in use in various industries as they have simple designs and can be built at a relatively low capital cost and are durable(Passas & Dunnill, 2015;Phillips, Edwards et al, 2017;Mulla & Dunnill, 2019). To start electrolysis process, a DC electric supply is passed through an electrolytic solution, splitting water (H 2 O) into its component parts (hydrogen (H 2 ) & oxygen (O 2 )) where H 2 being generated on the cathode and O 2 on the anode(Figure 3).…”