The Electroless Coupled Exchange Reduction Oxidation Process (eXERO™ Process) capitalizes on both the advantages of electrochemical processes (which yield high product purity without the need for expensive purification steps) and chemical processes (which have comparatively low capital and operating costs, especially avoiding the losses of electricity generation and transmission). The eXERO™ Process is achieved by removing the external electrical circuit from an electrolyzer and instead driving the electrolysis reaction with the overpotential (voltage) that exists between different gas compositions. Similar to a conventional solid oxide electrolyzer, oxygen ions are transferred from the cathode to the anode through an oxygen ion conducting electrolyte. However, unlike a conventional electrochemical reactor, electrons are transferred from the anode to the cathode through an electronically conducting phase within the electrolyte, also known as a mixed conducting electrolyte.
As of 2020, global annual hydrogen production amounted to approximately 87 million tons, with an estimated hydrogen generation market size valued at approximately $130 billion. Because of the high cost of hydrogen produced via electricity and the scale at which electrolyzers are currently available, only 4 % of the world’s hydrogen production is from electrolysis. The vast majority of the world’s hydrogen production today is derived from Steam Methane Reforming (SMR) and coal gasification, primarily in centralized locations. These processes typically involve three central steps – 1) the conversion of the hydrocarbon feed to synthesis gas (largely a mixture of hydrogen and carbon monoxide), 2) a water-gas shift reaction to convert carbon monoxide and steam to hydrogen and carbon dioxide, and 3) a purification step generally based on pressure swing adsorption.
Against the backdrop of the energy transition, the demand for hydrogen is projected to undergo profound change in its applications and experience enormous growth over the next decades. The reason for this is its anticipated adoption as a low carbon intensity transport fuel and for industrial and domestic refueling. The purity of hydrogen as a transport fuel is strictly controlled, as governed by ISO 14687:2019. This necessitates that carbon monoxide and sulphur-containing species be present at a concentration lower than 0.2 ppm and 4 ppb, respectively. To achieve this purity requires a more stringent separation process than those used conventionally to produce hydrogen. As of 2020, conventional purity requirements for the refining and other industrial processes are 97-99.9 %, which dominate the hydrogen market.
Figure 1. Global hydrogen demand in Mton, by sector. Light and dark blue are Refining and Industrial, respectively. Purple represents grid-injection for heat, ammonia for fuel in yellow. Light green represents hydrogen for transport fuel, and dark green represents hydrogen fuel for (stationary) power. Reproduced from IEA ‘Hydrogen’ https://www.iea.org/reports/hydrogen.
Hydrogen produced by water electrolysis is inherently at higher purity as it is generated directly from water and not syngas. Costly separation equipment such as pressure swing adsorption units are not required. The purity of hydrogen from electrolysis is reported to reach 99.999 % on a dry basis, compatible with ISO 14687:2019.
The state-of-the-art electrolyzer technologies can be differentiated based on their operating temperature:
- Low temperature (up to 100 ℃) devices: PEM, Alkaline; operating with liquid water
- High temperature (up to 1000 ℃) devices: Solid Oxide; operating with steam
The electrical energy to operate electrolyzers is drawn from electrical energy grids. The majority of the energy grids in the USA through 2050 are expected to continue to be largely powered by fossil fuels or nuclear energy. Consequently, when hydrogen is produced from the grid, significant emissions are produced, while significant inefficiencies are introduced in electricity production, transmission, and distribution.
The additional hydrogen demand, as shown in Figure 1, equates to approximately 110 million tons per year by 2050, with an equivalent energy content of 3.6 trillion kilowatt hours per annum. Assuming the average US electrical efficiency in 2019 of 36.8%, including transmission and distribution losses (2019 data), and a 67 % electrolysis efficiency, this equates to 14.6 trillion kWh of power required, which is 3.6 times the current total power being generated in the United States. In order to produce hydrogen with a low carbon intensity, this additional power requirement has to come from renewables. However, even accounting for the higher efficiency of renewables (and corresponding reduction in power generation requirement), installing this level of renewable power generation exceeds 2050 forecasts in figure 2 by several fold. Direct conversion of primary sources of energy and waste gases to hydrogen using the eXEROTM Process significantly reduces inefficiencies, in turn reducing the demand for primary source energy. It also preserves the benefits of high purity hydrogen production by electrolysis while simultaneously eliminating the costs, inefficiencies, variability, and supply limitations of renewable electricity. The eXERO™ Process is also highly feedstock flexible. The ability to process a variety of feedstocks, including waste gases plays an important role in decarbonizing the industrial sector. Industrial processes emit nearly 14.8 billion tons of CO2 per annum. The steel industry alone emits 3.7 billion tons of CO2 per annum. Waste gases from these industrial processes are challenging to utilize, and in many cases are used either for low value heating or flared. This is because these waste streams are generally low calorific, have varying flow and composition, and are often dilute. A reactor based on the eXERO Process permits the production of high value hydrogen from these waste streams, reducing primary source energy demand in the future.
The eXERO Process™ is based on two streams which are separated by an impermeable electrolyte, and counter-exchange of oxygen ions and electrons. Thus, one of the streams undergoes reduction while the other stream simultaneously undergoes oxidation. Unlike traditional fuel cells or electrolyzers, no current is extracted or delivered to the reactor to drive the process. Rather, an overpotential can be induced by introducing gases of different composition at the anode and cathode the cell. Examples of gases introduced at the anode to induce an overpotential, relative to steam (water) are shown below:
A simple example is introduction of pure carbon monoxide at the anode and pure steam at the cathode. The overall reaction occurring when carbon monoxide is used as the fuel is:
The overpotential for the final reaction occurs due to a wide concentration difference in H2 / H2O at the anode and at the cathode which seeks to bring itself to equilibrium via electrochemical reactions.
Alternatively, carbon dioxide may be reduced spontaneously at the cathode, with certain anode feed compositions, via the following reaction (anodic reactions remain identical):
The Nernst Equation can be used to calculate an overpotential generated across an electrolyte for varying gas atmospheres, as the electrical short circuit necessitates a cell potential difference of zero Volt. Therefore, with certain chemical compositions at the anode, steam in the cathode will spontaneously dissociate into hydrogen ions and oxygen ions. Using an oxygen ion conducting electrolyte to separate the two streams, oxide ions can therefore be spontaneously driven across the electrolyte. As in a traditional solid oxide electrolyzer with an applied external overpotential, simultaneously, electrons flow from the anode to the cathode, forming hydrogen at the cathode.
When electricity production is not desired and hydrogen is the only product, the traditional stack required by standard fuel cells and electrolyzers is no longer required. A mixed conducting electrolyte is used to transport both electrons from the anode to the cathode and oxygen ions from the cathode to the anode in the eXERO Process, enabling simpler and more robust architectures with the elimination of electrical continuity between cells.
The first patent application covering the eXERO™ Process was filed on April 26, 2019 with the United States Patent Office by Dr. Nicholas Farandos, Dr. Matthew Dawson, Dr. Jin Dawson, and Dr. David Hall.
1780 – Felice Fontana discovered the water gas shift reaction.
1800 – William Nicholson and Anthony Carlisle electrolyzed water.
1888 – Walther Hermann Nernst developed the Nernst Equation.
1937 – Emil Baur pioneered the solid oxide fuel cell.
2019 – Nicholas Farandos, Matthew Dawson, Jin Dawson, and David Hall applied for a patent on the eXERO™ Process4].
Utility Global, Inc., headquartered in Houston, Texas, is the only sustainable hydrogen company pioneering the eXERO™ Process to rapidly unlock a beyond-net-zero low carbon future. Initial commercial applications of the eXERO™ Process have targeted hydrogen production from waste gas streams using the H2GenTM product. With the technical and economic advantages cited, the eXERO™ Process can economically convert a number of waste gas streams to high purity hydrogen, including:
- Steel Waste – blast furnace gas, basic oxygen furnace gas
- Biowaste – biogas, dairy digester gas, municipal waste gas
- Renewable Natural Gas
- Refinery & Industrial Waste – flexicoker gas, fluid catalytic cracker gas, flue gases
The opportunity to convert waste gases into hydrogen is significant. As an example, if the eXERO™ Process was used to convert the world’s blast furnace and basic oxygen furnace steel waste gases into hydrogen, approximately 40 million tons/year of hydrogen could be produced, which equates to nearly half of the world’s current hydrogen production1. The eXERO™ Process may also be used to convert ammonia into fuel cell grade purity hydrogen. Partially cracked ammonia is used in the anode to produce high purity hydrogen from steam in the cathode of the eXERO™ Process. Unlike traditional processes, since the ammonia stream is intrinsically separated from the hydrogen stream in the eXERO™ Process, the hydrogen stream remains uncontaminated with residual ammonia. Today’s state-of-the-art ammonia cracking processes typically use ruthenium, iron, or nickel-based catalysts to crack ammonia into hydrogen. However, this traditional process route results in residual amounts of uncracked ammonia and nitrogen in the product hydrogen20. Even trace concentrations of ammonia in a PEM fuel cell can cause rapid degradation. Alternatively, if the hydrogen is to be liquefied, which is typically the case for road transport, low concentrations of NH3 and N2 will freeze in the liquefaction process, damaging the equipment. The residual ammonia from traditional cracking processes must therefore be removed through a secondary process, often involving an expensive palladium-based catalyst, to reach liquefaction and fuel cell grade purity20. The eXERO™ Process avoids this complexity altogether.
- Collins, Leigh (2021-05-18). “A net-zero world ‘would require 306 million tonnes of green hydrogen per year by 2050’: IEA | Recharge”. Recharge | Latest renewable energy news. Archived from the original on 2021-05-21.
- IEA ‘Hydrogen’ https://www.iea.org/reports/hydrogen
- ISO 14687:2019 Hydrogen fuel quality — Product specification https://www.iso.org/standard/69539.html
- Shell “Use and Optimization of Hydrogen at Oil Refineries” https://www.energy.gov/sites/prod/files/2017/05/f34/fcto_may_2017_h2_scale_wkshp_lafleur.pdf. Accessed 19 April 2022.
- S. S. Kumar, V. Hamabindu “Hydrogen production by PEM water electrolysis – A review” Materials Science for Energy Technologies 2019, 3, 2, 442, 454.
- U.S. Energy Information Administration “EIS Projects Renewables Share of US Electricity Generation Mix will Double by 2050”. Available at https://www.eia.gov/todayinenergy/detail.php?id=46676. Accessed April 2021.
- ITM Power “HGas1SP”. Available at: https://www.itm-power.com/hgas1se. Accessed May 2021