DETERMINING A PROPORTION OF HYDROGEN IN A MIXTURE OF HYDROGEN AND NATURAL GAS

Methods and apparatus for sensing hydrogen in a mixture of hydrogen and natural gas are provided. One example of the apparatus comprises: a first chamber for receiving air; a second chamber for receiving the mixture of hydrogen and natural gas; a first electrode for adsorbing oxygen molecules from air in the first chamber and for reducing the oxygen molecules to oxide ions; a second electrode; an ionic conductor for transporting the oxide ions from the first electrode to the second electrode in order to cause the transported oxide ions to combine with hydrogen molecules at the second electrode; sensing circuitry for sensing an electrical parameter associated with the combination of the transported oxide ions with the hydrogen molecules at the second electrode; and processing circuitry configured to determine a proportion of hydrogen in the mixture, based at least in part on the electrical parameter sensed by the sensing circuitry.

TECHNOLOGICAL FIELD

Embodiments of the present disclosure relate to determining a proportion of hydrogen in a mixture. Some relate to determining a proportion of hydrogen in a mixture of hydrogen and natural gas.

BACKGROUND

It has been identified that greenhouse gas emissions can be reduced by blending natural gas with hydrogen, thereby reducing the quantity of hydrocarbons that are present in a given volume of gas. It is currently thought that such blends might initially include around 1-2% of hydrogen, before being increased to 10-20% at a later date.

Industrial users may wish to determine the proportion of hydrogen in a hydrogen-natural gas blend so that they can account for it in their industrial processes.

The blending of hydrogen with natural gas produces a mixture with a calorific value that is different from that of the natural gas. In circumstances in which it is desirable to align the calorific value of such a blend with the monetary value (for example, if one wishes to attribute a higher price to a blend with a higher calorific value), then one may wish to determine the proportion of hydrogen in the blend in order to attribute an appropriate monetary value.

BRIEF SUMMARY

According to various, but not necessarily all, embodiments there is provided an apparatus for determining a proportion of hydrogen in a mixture of hydrogen and natural gas, the apparatus comprising: a first chamber for receiving air; a second chamber for receiving the mixture of hydrogen and natural gas; a first electrode for adsorbing oxygen molecules from air in the first chamber and for reducing the oxygen molecules to oxide ions; a second electrode; an ionic conductor for transporting the oxide ions from the first electrode to the second electrode in order to cause the transported oxide ions to combine with hydrogen molecules at the second electrode; sensing circuitry for sensing an electrical parameter associated with the combination of the transported oxide ions with the hydrogen molecules at the second electrode; and processing circuitry configured to determine a proportion of hydrogen relative to natural gas in the mixture, based at least in part on the electrical parameter sensed by the sensing circuitry.

According to various, but not necessarily all, embodiments there is provided a method for determining a proportion of hydrogen in a mixture of hydrogen and natural gas, the method comprising: receiving air in first chamber; adsorbing oxygen molecules from air in the first chamber and reducing the oxygen molecules to oxide ions using a first electrode; transporting the oxide ions from the first electrode to a second electrode using an ionic conductor; receiving the mixture of hydrogen and natural gas in a second chamber; combining the oxide ions with hydrogen molecules at the second electrode; sensing an electrical parameter associated with the combination of the transported oxide ions with the hydrogen molecules at the second electrode; and determining a proportion of hydrogen relative to natural gas in the mixture, based at least in part on the sensed electrical parameter.

According to various, but not necessarily all, embodiments there is provided an apparatus for sensing hydrogen in a mixture of hydrogen and natural gas, the apparatus comprising: a first chamber for receiving air; a second chamber for receiving the mixture of hydrogen and natural gas; a first electrode for adsorbing oxygen molecules from air in the first chamber and for reducing the oxygen molecules to oxide ions; a second electrode; an ionic conductor for transporting the oxide ions from the first electrode to the second electrode in order to cause the transported oxide ions to combine with hydrogen molecules at the second electrode; and sensing circuitry for sensing an electrical parameter associated with the combination of the transported oxide ions with the hydrogen molecules at the second electrode.

According to various, but not necessarily all, embodiments there is provided a method for sensing hydrogen in a mixture of hydrogen and natural gas, the method comprising: receiving air in first chamber; adsorbing oxygen molecules from air in the first chamber and reducing the oxygen molecules to oxide ions using a first electrode; transporting the oxide ions from the first electrode to a second electrode using an ionic conductor; receiving the mixture of hydrogen and natural gas in a second chamber; combining the oxide ions with hydrogen molecules at the second electrode; and sensing an electrical parameter associated with the combination of the transported oxide ions with the hydrogen molecules at the second electrode.

According to various, but not necessarily all, embodiments there is provided an apparatus for determining a proportion of hydrogen in a mixture of hydrogen and natural gas, the apparatus comprising: a first electrode; a second electrode; an ionic conductor for transporting charge carriers from the first electrode to the second electrode; sensing circuitry for sensing an electrical parameter associated with the transportation of charge carriers to the second electrode; and processing circuitry configured to determine a proportion of hydrogen relative to natural gas in a mixture, based at least in part on the electrical parameter sensed by the sensing circuitry.

DETAILED DESCRIPTION

Embodiments of the invention relate to an apparatus for determining a proportion/concentration (such as a molar concentration) of hydrogen in a mixture of hydrogen and natural gas (otherwise known as a hydrogen-natural gas blend). The apparatus comprises an electroceramic cell that is sensitive to hydrogen. An electric current output by the electroceramic cell depends on the proportion of hydrogen in a given volume of a mixture of hydrogen and natural gas. Consequently, the output electric current can be used to determine the proportion of hydrogen that is present in the mixture.

Advantageously, once the proportion of hydrogen in the mixture has been determined, industrial users are able to adapt their industrial processes (e.g. in glass-making) to account for it and/or an appropriate monetary value can be attributed to the mixture.

FIG.1illustrates a schematic of the apparatus100. In the illustrated example the apparatus100comprises a first chamber10, a first (reference) electrode/cathode20, an ionic conductor30, a second (sensing) electrode/anode40, a second chamber50, sensing circuitry60, at least one processor/processing circuitry70and memory80.

The first electrode20, the ionic conductor30and the second electrode40collectively form an electroceramic cell45.FIGS.2A,2B and2Cillustrate a first side view, a second side view and a perspective view of the electroceramic cell45respectively.

The ionic conductor30might, for example, be a ceramic ionic conductor such as a ceramic electrolyte. The ceramic electrolyte30might, for example, be made at least in part from gadolinium-doped ceria (GDC), samarium doped ceria, scandia stabilised zirconia, lanthanum strontium gallium magnesium or yttria-stabilised zirconia (YSZ), such as 8YSZ. A ceramic electrolyte30is particularly suitable for use in the apparatus100, facilitating the imposing of conditions and pairing the electrodes20,40, in order to demonstrate a high selectivity of hydrogen over methane.

The (ceramic) ionic conductor30might be or comprise a (ceramic) semiconductor material. For example, the ionic conductor30may be a (ceramic) semiconductor material such as a metal oxide (e.g. tin oxide) or a metalloid oxide (e.g. silicon dioxide). The (ceramic) semiconductor material may be doped. Such a (doped, ceramic) semiconductor30might be used instead of a ceramic electrolyte as described above or in combination with such a ceramic electrolyte.

The ionic conductor30might be substantially planar in shape, as illustrated inFIGS.2A,2B and2C. The ionic conductor30has a length L, a width W and a depth D. The length L might be the same as or greater than the width W. The length L and the width W are greater than the depth D. The ionic conductor30might be relatively compact in size. For example, in some embodiments the length L and the width W might each be approximately 50 mm and the depth D might be approximately 200 μm. It will be appreciated by those skilled in the art that other sizes are possible.

The first and second electrodes20,40are electrically conductive. The first electrode20is positioned on a first surface/face32of the ionic conductor30. The second electrode40is positioned on a second surface/face34of the ionic conductor30. Each of the first and second surfaces are defined by the length L and the width W of the ionic conductor30. The first and second electrodes20,40are on opposite surfaces32,34of the ionic conductor30in that they are separated by the depth D of the ionic conductor30.

In some embodiments, one or both of the first and second electrodes20,40is a thin film. The first and second electrodes20,40might be deposited or coated on the first and second surfaces32,34of the ionic conductor30such as by using screen printing or sputter vapour deposition techniques. It is preferable that the thickness of the thin films be sufficient to ensure durability and prevent atomisation. It has been found that a thickness of the order of 250 nm is suitable.

The first and second electrodes20,40are porous. The patterning is such that at least a portion of the first and second surfaces32,34of the ionic conductor30remain uncovered (within the outer boundary of each of the electrodes20,40) to enable gas ingress into the ionic conductor30. In addition, in the illustrated example an area31,33around the outer boundary of the electrodes20,40at periphery of each of the first and second surfaces32,34is uncovered. This area31,33may be used to seal the electroceramic cell45within the apparatus100. This is described later.

A mask may be used to form the first and/or second electrodes20,40in a particular pattern. In one example, a porous foam or mesh is used as a mask in a sputtering process to scatter a deposited film on the first and second surfaces of the ionic conductor30.

In some alternative examples, the first and second electrodes20,40might not be thin film electrodes. The electrodes20,40might instead be formed using a slurry or an equivalent mixture and might therefore be thicker in nature. In this regard, each of the first and second electrodes20,40might be made from a combination of a nanostructured bed/scaffold and one or more catalysts. For instance, the first and second electrodes20,40might be made from a cermet (a composite of ceramic and metal) or a ceramic semiconductor doped with the metallic compound. The ceramic material in the cermet might be the same material that the ionic conductor30is formed from, including the ceramic-semiconductor mixtures. It is preferable that the metal/catalyst loading within the electrode20,40is sufficient so as to fulfil the requirement of durability, in the order of 1 mg/cm2or greater.

A scaffold bed may also be used to form the porous backbone of each of the electrodes20,40. This scaffold may be made out of the same ceramic material as the electrolyte/semiconductor30. Thereafter, the required amount of catalyst compound may be deposited or infiltrated into the scaffold to form an electrode20,40with a suitable porosity.

The first electrode20may be made, at least in part, from at least one of: platinum, silver, nickel, lanthanum strontium manganite or lanthanum strontium cobalt ferrite.

It has been determined that the use of these materials for the first electrode20is advantageous in that they have a high thermochemical stability such that they produce a similar current for a given voltage and oxygen concentration.

The second electrode40may be made, at least in part, from at least one of: platinum, gold, silver, rhodium or lanthanum strontium cobalt ferrite.

It has been determined that use of these materials for the second electrode40is advantageous in that they: (i) provide enhanced selectivity to process hydrogen adsorption and surface reactions over competing reactions such as methane oxidation, reforming, etc.; (ii) demonstrate a high resistance to carbon deposition on the electrode, such that operation of the electroceramic cell45remains uninhibited over time and retains a known/expected sensitivity to hydrogen; (iii) are compatible with ceramic electrolytes such as GDC and YSZ (if such a ceramic electrolyte is used), thereby enhancing the high resistance to carbon deposition described above in (ii); (iv) demonstrate a high tolerance to the presence of possible corrosive elements such as H2S in the mixture; and (v) remain operational in expected the operating conditions and mixtures that they are exposed to.

In one combination, the first electrode20is formed from at least in part from platinum, the ionic conductor30is formed from GDC and the second electrode40is formed at least in part from gold. This is an example of an asymmetric cell45because the electrodes20,40are formed at least in part from different materials. In another combination, the first and second electrodes20are formed from silver and the ionic conductor30is formed from YSZ. This is an example of a symmetric cell45because the electrodes20,40are formed from the same material.

FIG.3illustrates an exploded perspective view of an example of an assembly1000forming at least part of the apparatus100. In this particular example, the assembly1000includes the first and second chambers10,50and the electroceramic cell45illustrated inFIG.1, but the assembly1000does not comprise the sensing circuitry60, the processing circuitry70or the memory80, which are provided separately.

The assembly100comprises a housing200that defines the first and second chambers10,50. The housing200comprises a first housing part8and a second housing part58. The housing200is formed is attaching the two housing parts8,58to each other. The first chamber10has a fixed volume and is located in/defined by the first housing part8. The second chamber50has a fixed volume and is defined by/located in the second housing part58. Each of the first and second housing parts8,58have the same shape in this example, such that the fixed volumes of the first and second chambers10,50are the same. This might or might not be the case in other examples.

Each of the first and second housing parts8,58might be formed from at least one ceramic in order to provide the housing parts8,58with thermal properties that closely match the electroceramic cell45. Alternatively, the electroceramic cell45might be externally supported by fabrication on a ceramic substrate to compact the assembly and improve electrochemical performance.

In the illustrated example, each of the housing parts8,58comprises an inlet2,52and an outlet4,54. The inlet2in the first housing part8enables air to be received in the first chamber10and the outlet4in the first housing part8enables air to be output from the first chamber10. The inlet52in the second housing part58enables an analyte gas in the form of a mixture of hydrogen and natural gas to be received in the second chamber50and the outlet54in the second housing part58enables the mixture to be output from the second chamber50.

The electroceramic cell45is secured between the first and second housing parts8,58. An (internal) opening7is illustrated in the first housing part8inFIG.3. A first seal/gasket92is positioned around the opening7in the first housing part8and around the first electrode20in the electroceramic cell45. For instance, the first seal92can be positioned on the peripheral area31of the first surface32of the ionic conductor30.

The second housing part58also includes an (internal) opening which, though not shown inFIG.3, corresponds with the opening7in the first housing part8. A second seal/gasket94is positioned around the opening in the second housing part58and around the second electrode40in the electroceramic cell45. For instance, the second seal94can be positioned on the peripheral area33of the second surface34of the ionic conductor30.

Each of the first and second seals92,94is a high temperature seal and might, for example, be made from Thermiculite® 866.

The opening7in the first housing part8enables air/oxygen to pass from the first chamber10and into electroceramic cell45via its first surface32comprising the first electrode20. The opening in the second housing part58enables hydrogen and natural gas to pass from the second chamber50and into electroceramic cell45via its second surface34comprising the second electrode40. The first and second electrodes20,40are isolated from one another in the assembly1000. The first and second chambers10,50are shaped and positioned in the assembly such that the air in the first chamber10is isolated from the mixture of hydrogen and natural gas in the second chamber50.

When the assembly1000is assembled, the electroceramic cell45is positioned in between the first and second housing parts8,58and sealed using the seals92,94. The first housing part8is then attached to the second housing part58.

It can be seen inFIG.3that an aperture58is provided in the second housing part58to provide an electrical connection to the second electrode40. A corresponding aperture (not shown inFIG.3) is also provided in the first housing part8to provide an electrical connection to the first electrode20.

The sensing circuitry60, the processing circuitry70and the memory80of the apparatus100illustrated inFIG.1are not shown inFIG.3. The sensing circuitry60and the processing circuitry70are operationally coupled together and any number of elements may exist therebetween (including no intervening elements). The sensing circuitry60is configured to sense an electrical parameter, such as electric current.

The processing circuitry70is configured to read from and write to the memory80. The memory80stores a computer program82comprising computer program instructions (computer program code). The processing circuitry70, by reading the memory80, is able to load and execute the computer program82. The processing circuitry70, under the control of the computer program, is configured to interpret the electrical parameter sensed by the sensing circuitry60. The computer program instructions of the computer program82provide the logic and routines carried out by the processing circuitry70. In some implementations, operation of the apparatus100might be controlled by the processing circuitry70based on the sensed electrical parameter.

The computer program instructions may be comprised in a computer program, a non-transitory computer readable medium, a computer program product, a machine readable medium. In some but not necessarily all examples, the computer program instructions may be distributed over more than one computer program.

Although the processing circuitry70is illustrated as a single component/circuitry it may be implemented as one or more separate components/circuitry some or all of which may be integrated/removable. The processing circuitry70may be a single core or multi-core processor.

Operation of the apparatus100will now be described in conjunction with the flow chart illustrated inFIG.4. In this example the sensing circuitry60is configured to apply a (fixed) potential difference across the first and second electrodes, ESE−ERE.

At block401inFIG.4, air is received in the first chamber10via the inlet2. As shown inFIG.1, the air includes oxygen and nitrogen. Some air is output via the outlet4. At block402inFIG.4, oxygen molecules in the air located in the first chamber10are adsorbed and reduced into oxide ions by the first electrode20. As illustrated inFIG.1, a reaction occurs at the first electrode20in which each oxygen molecule combines with four electrons at the first electrode20to form a negatively charged oxide ion.

At block403inFIG.4, the oxide ions (charge carriers) are conducted/transported by the ionic conductor from the first electrode20to the second electrode40. The conductivity of the ionic conductor30depends upon its temperature. As the temperature of the ionic conductor30increases, its ability to conduct oxide ions increases. In order to maintain sufficient ionic conductivity, it might be desirable to maintain the temperature of the ionic conductor30above a minimum temperature, such as 400° C. In some embodiments, the apparatus100might comprise one or more temperature sensors for sensing the temperature of the ionic conductor30. The apparatus100might further comprise one or more heating elements for heating the ionic conductor30, such as one or more thin film heating elements. The processing circuitry70might be configured to receive and analyse inputs from the temperature sensor(s). It might control the one or more heating elements to adjust the temperature of the ionic conductor30based on the inputs from the temperature sensor(s), in order to maintain the temperature of the ionic conductor30above the minimum temperature.

At block404inFIG.4, a mixture of hydrogen and natural gas is received in the second chamber50. The mixture of hydrogen and natural gas may be received in the second chamber50before, after, or at the same time that air is received in the first chamber10. The natural gas includes one or more hydrocarbons, such as methane, ethane, propane, butane and pentane. In the example illustratedFIG.4, it is assumed for simplicity that the natural gas includes methane (CH4) but not ethane, propane, butane or pentane. Hydrogen molecules and methane molecules in the mixture received by the second chamber50are adsorbed by the second electrode40.

At block405inFIG.4, a reaction occurs at the second electrode40in which oxide ions that have been transported from the first electrode20to the second electrode40combine with hydrogen and methane molecules. The combination of a hydrogen molecule with an oxide ion produces water and two electrons. The combination of a methane molecule with four oxide ions produces carbon dioxide, water and eight electrons. The potential difference applied by the sensing circuitry60causes the electrons that were produced by the reaction at the second electrode40to flow to the first electrode10, generating an electric current directed from the first electrode10to the second electrode40. The magnitude of the electric current that is generated, for a given applied potential difference, depends on the catalytic activity that occurs at the second electrode40. The amount of catalytic activity that occurs at the second electrode is dependent on the proportion of hydrogen in the mixture of hydrogen and natural gas. The greater the proportion of hydrogen in the mixture relative to natural gas/methane, the greater the level of catalytic activity.

At block406inFIG.4, the sensing circuitry60senses an electrical parameter associated with the combination of the transported oxide ions with the hydrogen molecules at the second electrode40, and provides corresponding inputs to the processing circuitry70. In some examples, the electrical parameter may be electric current that is produced, at least in part, from the combination of the transported oxide ions with the hydrogen molecules at the second electrode40.

At block407inFIG.4, the processing circuitry70determines a proportion/concentration of hydrogen relative to natural gas in the mixture, based at least in part on the electrical parameter sensed by the sensing circuitry60. In some embodiments, the processing circuitry70might determine a calorific value for the mixture based on the determined proportion of hydrogen. The processing circuitry70might control a display to display the determined calorific value.

FIG.5illustrates a graph showing the electric current measured/sensed by the sensing circuitry60when inputting various mixtures having varying amounts of methane (CH4) and hydrogen (H2) and a fixed amount of nitrogen (N2) into the second chamber50of the apparatus100over a period of time.

The graph illustrates the electric current that was measured for various different ratios of methane to hydrogen. The nitrogen is inert and does not react with the first electrode20. It will be appreciated that in some examples nitrogen might not be present, and that the methane could be replaced or supplemented by one or more of ethane, propane, butane and pentane.

In this example, the processing circuitry70is configured to determine a proportion of hydrogen relative to natural gas in the mixture, based at least in part on the electric current sensed by the sensing circuitry60. A look-up table may be stored in the memory80which associates particular values of electric current with particular proportions of hydrogen. For instance, in the illustrated example, if an electric current of approximately 45 mA were sensed by the sensing circuitry60, the processing circuitry70would determine by referring to the look-up table that the proportion of hydrogen in the mixture is approximately 4.2%. If, for instance, the sensed electric current were approximately 100 mA, the processing circuitry70would determine by referring to the look-up table that the proportion of hydrogen in the mixture is approximately 12.5%.

As indicated inFIG.5, the temperature of the ionic conductor30was determined to be approximately 500° C. when the electric current measurements were obtained, and the potential difference applied by the sensing circuitry60across the first and second electrodes20,40was +0.4V. It will be appreciated by those skilled in the art that the sensed electric current is proportional to the applied potential difference. Thus, a fixed potential different might be applied across the first and second electrodes20,40to obtain consistently accurate measurements. The processing circuitry70might be configured to control the sensing circuitry60to alter the applied potential difference. In such embodiments, where different potential differences might be applied in different circumstances, a different look-up table associating sensed electric currents with particular proportions of hydrogen might be provided for each (possible) applied potential difference.

As explained above, the ionic conductivity of the ionic conductor30depends on its temperature. Thus, the processing circuitry70might be configured to determine the proportion of hydrogen in the mixture based at least in part on at least one input provided by one or more temperature sensors of the apparatus100. For instance, a different look-up table associating sensed electric currents with particular proportions of hydrogen might be provided for particular temperatures or temperature ranges. In the event that different potential differences are applied across the first and second electrodes20,40, a particular look-up table might relate to a particular potential difference and temperature/temperature range.

FIG.6Aillustrates an example in which an array22of temperature sensors22a-22iis positioned at the first surface32of the ionic conductor30, possibly with a portion of the first electrode20therebetween. The first array22of temperature sensors22a-22imight be integrally formed with the first electrode20.

In the illustrated example, the temperature sensors22a-22iin the array22are spatially distributed in two dimensions across the length L and width W of the first surface32of the ionic conductor30. The temperature sensors22a-22iare ordered in a grid in FIG.6A, but need not be in other implementations. In some examples, the temperatures sensors22a-22imight instead be spatially distributed in a single dimension only (the length dimension L or the width W dimension).

FIG.6Billustrates an example in which an array42of temperature sensors42a-42iis positioned at the second surface34of the ionic conductor30, possibly with a portion of the second electrode40therebetween. The array42of temperature sensors42a-42imight be integrally formed with the second electrode40. In the illustrated example, the temperature sensors42a-42iin the array42are spatially distributed in two dimensions across the length L and width W of the second surface34of the ionic conductor30. The temperature sensors42a-42iare ordered in a grid inFIG.6B, but need not be in other implementations. In some examples, the temperatures sensors42a-42imight instead be spatially distributed in a single dimension only (the length dimension L or the width W dimension).

The temperature sensors22a-22i,42a-42imay provide temporal temperature sensing and spatial temperature sensing. Spatially, the temperature sensors22a-22i,42a-42iprovide three-dimensional temperature sensing because they are spatially distributed across the electrodes20,40in the length L and width W dimensions of the ionic conductor30and the two arrays22,42are spatially distributed in the depth D dimension of the ionic conductor30.

The processing circuitry70receives and monitors (spatial and/or temporal) inputs from the temperature sensors22a-22i,42a-42i. Increases in temperature will occur due to electrochemical activity in the ionic conductor30and catalytic activity at the electrodes20,40. The processing circuitry70can determine from the inputs whether one or more portions of the electroceramic cell45and/or the electrodes20,40are heating up more quickly than others. For instance, the reactions taking place at the second electrode40are exothermic in nature. If the temperature sensors42a-42iat the second electrode40indicate that one or more portions of the second electrode50are heating up more quickly than one or more other portions of the second electrode40, that might indicate that those other portions are defective or that there is a flow restriction in the ionic conductor30that is preventing oxide ions from reaching those other portions of the second electrode40.

The processing circuitry70may monitor the inputs from each temperature sensor42a-42iat the second electrode42aand, if the temperature differential reaches a threshold, the processing circuitry70might cause an alert to be provided to a user. For example, the processing circuitry70might be operationally coupled to a display and/or a loudspeaker and might cause a visual alert and/or an aural alert to be provided to the user.

Corresponding functionality to that described above may be provided in relation to the temperature sensors22a-22iat the first electrode20/first surface32of the ionic conductor30.

The inputs from temperature sensors22a-22i,42a-42ion each side of the ionic conductor30provide the processing circuitry70with a through-depth view of temperature distribution. This might enable the processing circuitry70or a user to determine which side is the bottleneck or the cause in the event that the electric current output by the electroceramic cell45is deviant, sluggish, erratic etc.

If there is an abnormally large temperature differential across the depth of the ionic conductor30(e.g. 30-60° C.), it is likely to be indicative of gas leakage from the first chamber10to the second chamber50or from the second chamber50to the first chamber10. This facilitates local combustion leading to a temperature spike well above the nominal operating temperature of the ionic conductor30, accounting for the increment in temperature that occurs from electrochemical activity at the electrodes20,40. By having at least one temperature sensor22a-22i,42a-42ion each side of the electroceramic cell45, it is possible to determine which side the combustion is taking place on, as that/those temperature sensors22a-22i,42a-42iwill sense a higher temperature (though there will also be a lower rise/spike in temperature at the other electrode20,40).

If one or more temperature sensors42a,42b,42c,42d,42f,42g,42h,42ilocated proximate an edge of the electrode40/ionic conductor30sense a higher temperature than one or more temperature sensors42clocated away from that edge, it might be indicative of sealing failure. If at least one temperature sensor42clocated in or proximate the middle of the surfaces32,34of the electroceramic cell45senses a higher temperature than the others, it might be indicative of cracking of the ionic conductor30.

As described above, by monitoring the inputs from temperature sensors22a-22i,42a-42i, analysing how each one varies over time and/or comparing the inputs from different temperature sensors22a-22i,42a-42ireceived at substantially the same time with one another, the processing circuitry70can identify a difference that exceeds a threshold and respond by causing a (visual and/or aural) alert to be provided to a user. In some examples, the processing circuitry70might merely cause the sensed temperatures from the temperature sensors22a-22i,42a-42ito be provided by a user (e.g. displayed on a display) and the user might then interpret the sensed temperature(s).

It was explained above that there might be a preferred minimum operating temperature for the ionic conductor30. In some embodiments, a plurality of heating elements might be distributed in two or three dimensions in the apparatus100(such as in the chambers10,50). The temperature inputs from temperature sensors that are spatially distributed in two or three dimensions might be used by the processing circuitry70as a basis to control heating in two or three dimensions, by causing individual heating elements to switch on, provide more heat, provide less heat or switch off.

As explained above, the temperature inputs provided by the temperature sensors22a-22i,42a-42iare indicative of the amount of electrochemical activity at each of the electrodes20,40. The processing circuitry70might be configured to control a flow rate of air into the first chamber10based at least in part on inputs received from one or more temperature sensors22a-22iat the first electrode20/first surface32of the ionic conductor30, and/or control a flow rate of the mixture into the second chamber50based at least in part on inputs received from one or more temperature sensors42a-42iat the first electrode20/first surface32of the ionic conductor30. This might be achieved by controlling one or more valves.

It may be desirable to limit the temperature of operation of the electrochemical cell45to a particular maximum temperature (e.g. 500° C.) in order to limit the amount of carbon deposition that occurs at the second electrode40. The maximum temperature limit may also aid in the health and preservation of the ionic conductor30, to limit its electronic conductivity and maintain its purely ionic transport. This will allow the apparatus to maintain the correlation of the hydrogen gas concentration to the electrical parameter based on the maintenance of the characteristic voltage-current relation. If the processing circuitry70determines that the electrochemical cell45, the first electrode20and/or the second electrode40has/have exceeded a particular maximum temperature, it might respond by switching off the cell45or reducing the catalytic and electrochemical activity at the cell45. The switching off of the cell45or a reduction in catalytic and electrochemical activity at the cell45could be achieved by preventing or reducing the amount of air entering the first chamber10, and/or preventing or reducing the amount of the mixture entering the second chamber50. The processing circuitry70might do this by controlling one or more valves.

References to a “computer”, “processor” or “processing circuitry” etc. should be understood to encompass not only computers having different architectures such as single/multi-processor architectures and sequential (Von Neumann)/parallel architectures but also specialized circuits such as field-programmable gate arrays (FPGA), application specific circuits (ASIC), signal processing devices and other processing circuitry. References to computer program, instructions, code etc. should be understood to encompass software for a programmable processor or firmware such as, for example, the programmable content of a hardware device whether instructions for a processor, or configuration settings for a fixed-function device, gate array or programmable logic device etc. References to computer program, instructions, code etc. should be understood to encompass artificial intelligence algorithms and, in particular, machine learning algorithms.

The blocks illustrated inFIG.4may represent steps in a method. The illustration of a particular order to the blocks does not necessarily imply that there is a required or preferred order for the blocks and the order and arrangement of the block may be varied. Furthermore, it may be possible for some blocks to be omitted.

Although examples have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the claims. For example, while two arrays22,42are illustrated inFIGS.6A and6Band described above, in some implementations there might not be any temperature sensors. In others, there might be a single temperature sensor, or a single temperature sensor on each side of the ionic conductor30.

The method described above in relation toFIG.4might further comprise a plurality of calibration steps in which known mixtures of gases are introduced into the second chamber50and associations are made between the sensed electrical parameter for each gas and the proportion of hydrogen. Those gases may be, or comprise, C1-C6 hydrocarbons with hydrogen of differing concentrations/proportions.

An example is described above in which the length L and the width W of the ionic conductor30are each 50 mm, and the depth is 200 μm. The proportion of hydrogen in the mixture that is detectable scales with the active area of the electroceramic cell45. Thus, if it is desired to detect the proportion of hydrogen in a mixture containing larger amounts of hydrogen (e.g. 20%), it may be appropriate to use a larger electroceramic cell45.

One or more valves may be provided to control the flow of air into the first chamber10. This/these valve(s) may be controlled by the processing circuitry70. One or more valves may be provided to control the flow of the mixture into the second chamber50. This/these valve(s) may be controlled by the processing circuitry70. If, for example, the electric current that is produced is undesirably low, the processing circuitry70might control one or more valves to increase the flow of air into the first chamber10and/or the flow of the mixture into the second chamber50. The control will depend on where the rate-limiting reaction is occurring; if it is at the first electrode20, an increase in the flow of air may be desirable, whereas if it is at the second electrode40, an increase in the flow of the mixture may be desirable. In some embodiments, the processing circuitry70might (automatically) control the flow of air into the first chamber10and/or the flow of the mixture into the second chamber50based on the sensed electrical parameter.

Although implementations are described above in which a potential difference is applied across the electrodes20,40by the sensing circuitry60, in other examples no such potential difference is applied. Instead the electroceramic cell45might be operated in open circuit voltage (OCV) mode. In such a mode, electric current might still be used as the metric for determining the proportion of hydrogen in the mixture. In OCV mode the electroceramic cell45may have a self-generated work potential and a variable resistor can be used to maintain that potential at a fixed level.

It is explained above that electric current is produced, at least in part, from the combination of transported oxide ions with hydrogen molecules at the second electrode40. The electrical parameter that is sensed by the sensing circuitry60is described above as being the electric current itself. However, the electrical parameter that is sensed by the sensing circuitry60might be a different electrical parameter, such as a potential difference or an impedance/resistance.

For example, in alternative implementations, the electroceramic cell45may respond to the changes in relative concentrations of hydrogen and methane with recourse to the characteristic impedance and frequency-dependant properties of the respective gas quantities and their associated reactions. Here, in these implementations, the electroceramic cell45might be operated in an applied potential current mode or an OCV mode. The impedance spectra may be obtained with the plotting of real and imaginary components of the impedance across a frequency range, known as the Nyquist plot. Based on the appropriate deconvolutions and equivalent circuit specification, the mixture proportion may be ascertained by the parameters and properties of the circuit, such as the characteristic charge transfer resistances, capacitances and relaxation time estimations.