Hydrogen fuel Quality requirements for transportation and other energy applications

Final Report Summary - HYQ (Hydrogen fuel Quality requirements for transportation and other energy applications)

HyQ consists of pre-normative studies to provide a strong support to Regulation Codes and Standards organisations in order to normalize an acceptable fuel quality for PEMFC. HyQ is focused on automotive application which requires high hydrogen quality for...

Executive Summary:

HyQ consists of pre-normative studies to provide a strong support to Regulation Codes and Standards organisations in order to normalize an acceptable fuel quality for PEMFC. HyQ is focused on automotive application which requires high hydrogen quality for high power delivery. Nevertheless, HyQ also deals with the stationary application.

Faced to the increased global energy demand and to environmental concerns, the concept of using hydrogen as fuel has shown a real potential. Proton Exchange Membrane Fuel Cells (PEMFC) appear to be the best hydrogen-based energy conversion devices for a wide range of applications from portable to vehicles. The performances and durability of such a device are affected by the quality of the reactive gases. Depending on the way to produce and purify hydrogen, it can contain different kind of pollutants which impact the performances and the durability of PEMFC. Standardization of the H2 quality is a pre-requisite for the hydrogen based energy technology enabling the industry to move towards a mass market.

The technical aspects of this project can be divided in three main parts. One part focuses on the impact of the impurities on the PEMFC depending on the end-users specification. The purpose of this part is to find out the maximum level of contaminants in H2 to stay in an acceptable range of PEMFC performances. The second part focuses on the analysis of H2 and the quantification of each contaminant in the fuel. The main objective of this task is to figure out the cheapest and most accurate method to assure the gas quality and the concentration of each impurity in H2. The third part consists on a cost benefit analysis based in the one hand on the hydrogen fuel production, purification and quality insurance cost depending on the quality required and in the second hand on the investment needs and the maintenance cost of a PEMFC according to the end user specifications. The goal of this cost benefit analysis is clearly to find out the optimum level of quality of H2; it means the level of quality which response to a consensus between gas producers (production/purification cost) and OEMs (PEMFC cost).

Thanks to the work plan define in the first period and after the choice of most relevant impurities to be tested made by the consortium, the final period of the project was focussed on PEMFC testing campaign.

Partners showed that on/off cycles are benefit to mitigate the impact of impurities and especially the ones which have a reversible impact. Indeed, after stopping and restarting the fuel cell and when feeding it with CO containing H2, a recovery of cell performances is observed. Furthermore, In that condition, the release of adsorbed pollutant from the catalyst has been observed by coupling a gas chromatograph analyser to the fuel cell.

Furthermore, the analytical tools developed by the consortium now allow quantifying the most relevant and challenging impurities in H2 (total sulphur compound and formaldehyde). The limit of quantification for total sulphur compound has reached 3.3 ppb (ISO standard highest acceptable level: 4 ppb). The limit of detection for formaldehyde has reached 5 ppb for formaldehyde and 10 ppb for formic acid which is, for formic acid, at least 20 times less than the highest acceptable level required by ISO.

The conclusions of the first period have been transmitted to the ISO. The consortium made recommendation thanks to the ISO mirror committee in which HyQ partners are members. They expressed their recommendation during the ballot of the document ISO TC 197, WG14 DIS 14687-3.

Project Context and Objectives:

HyQ consists of pre-normative studies to provide a strong support to Regulation Codes and Standards organisations in order to normalize an acceptable fuel quality for PEMFC. HyQ is focused on automotive application which requires high hydrogen quality for high power delivery. Nevertheless, HyQ also deals with the stationary application.

Faced to the increased global energy demand and to environmental concerns, the concept of using hydrogen as fuel has shown a real potential. Proton Exchange Membrane Fuel Cells (PEMFC) appear to be the best hydrogen-based energy conversion devices for a wide range of applications from portable to vehicles. The performances and durability of such a device are affected by the quality of the reactive gases. Depending on the way to produce and purify hydrogen, it can contain different kind of pollutants which impact the performances and the durability of PEMFC. Standardization of the H2 quality is a pre-requisite for the hydrogen based energy technology enabling the industry to move towards a mass market. Thanks to HyQ, Europe shows a strong involvement in the hydrogen fuel quality standardization process for vehicle PEMFC applications.

These pre-normative studies on the specification of hydrogen fuel quality result, in one hand, in validated methods to quantify the impact of hydrogen impurities on PEMFC and, in another hand, in the determination of acceptable levels of hydrogen contaminants to maintain performance and durability expected by the end-users. In parallel, another outcome of the HyQ project consists in validated sampling and analytical methods to measure and certify the hydrogen quality.

The technical aspects of this project can be divided in three main parts. One part focuses on the impact of the impurities on the PEMFC depending on the end-users specification. The purpose of this part is to find out the maximum level of contaminants in H2 to stay in an acceptable range of PEMFC performances. The second part focuses on the analysis of H2 and the quantification of each contaminant in the fuel. The main objective of this task is to figure out the cheapest and most accurate method to assure the gas quality and the concentration of each impurity in H2. The third part consists on a cost benefit analysis based in the one hand on the hydrogen fuel production, purification and quality insurance cost depending on the quality required and in the second hand on the investment needs and the maintenance cost of a PEMFC according to the end user specifications. The goal of this cost benefit analysis is clearly to find out the optimum level of quality of H2; it means the level of quality which response to a consensus between gas producers (production/purification cost) and OEMs (PEMFC cost).

The project has started with an assessment of H2 production based on production and purification schemes. The different H2 production process investigated were steam methane reforming (SMR), autothermal reforming, coal gasification, biomass gasification, water electrolysis and hydrogen from by-products. That allows the consortium to identify the most relevant pollutant species for each process. However a special emphasis has been put on SMR as it is the most common industrial process used to produce H2. By the most relevant species, the reader should understand the ones whose the actual standards is hardly achievable or the ones whose the concentration is hard to measure by actual method or the ones which dramatically impact the PEMFC performances. These critical impurities are CO, HCHO, NH3, H2S and halogenated compounds. Furthermore, economic data on the H2 price depending on its quality have been gathered to implement the cost-benefit analysis.

A review of the actual method of analyses available to measure the amount of each impurity in H2 has been performed. This has allowed the consortium to point out species for which the concentrations specified in the actual standards are hardly determined. The analysis of total sulphur compound (4ppb) seems to be the most important and most challenging specification to meet. A direct injection GC-SCD (gas chromatography - sulphur chemiluminescence detection) method is being developed to measure total sulphur compounds at low-ppb levels. This method, which uses a GC column with minimal retention, allows the analysis of total sulphur compounds without the need for pre-concentration (which is a significant advantage over the exiting ASTM method).

The partners have also highlighted that the current standards for total halogenated compound (50 ppb) represent a broad family of compounds. Measuring some halogenated compounds using CRDS (cavity ring-down spectroscopy) and FTIR (Fourier transform infrared) spectroscopy has been investigated, but it is still problematic. The definition of total halogenated compounds should be more restrictive to the species that could be found in H2.

This review has shown that the current standards on the formaldehyde (10 ppb) are very restrictive and its quantification is not easy with the actual method.

Most of the impurities present in H2 are analysed separately. To make the quality insurance more convenient, the consortium is working on a single method to analyse several pollutants using a single method.

A deep review of the public experimental data used to determine the current standards and/or data available in literature on the impact of pollutants from the H2 has also been performed. In this review, a special emphasis have been put on the experimental conditions and on the MEAs specifications. This was used by HyQ to propose operation condition under which the impact of pollutants has never been tested yet. Our choice has been to use steady state and dynamic load cycles to work under automotive and stationary application. The tests are performed using low anode Pt laoding MEAs to enhance the response of the MEAs towards pollutant and thus to diminish the experiment time. Use of low anode Pt loading MEAs allows us to anticipate the future developments that will be done by MEAs manufacturers.

The model for the cost-benefit analyses has been built. This model considers hydrogen production options available in the near term and very ‘small’ processes are excluded from this analysis. The entire production and purification processes are considered as a single block (production plant plus purification process). In a first step the model has focussed on CO as a single impurity of the fuel. The impact of different hydrogen purity levels (treated as an input) is modelled in terms of a variation in the capital and operating costs of the fuel cell system to deliver the same end-user performance.

The results from HyQ will be helpful for technical discussion concerning the last part of the standardization process of the hydrogen quality and also the revision of the current standard. Furthermore the project proposes conditions and method under which the other institutes could test the impact of pollutant on their own materials.

Project Results:

Identification of impurities of hydrogen for automotive PEMFC application:

In a first task, different industrial ways to produce H2 was analyse in order to point out the nature of the impurities species present in H2 before and after purification. This task was necessary in order to focus our intention on the impurities that really are present in H2. The H2 production processes studied were:

• Steam Methane Reforming

• Autothermal Reforming

• Coal gasification

• Biomass gasification

• Water electrolysis

• Hydrogen from by-products

The main conclusions of the study are:

Steam Methane Reforming is most likely to provide the Synthesis Gas with the lowest complexity concerning composition and impurities. It typically has lower inert gas content than other processes involving hydrocarbons, however significant amounts of He are found in some natural gas sources, particularly natural gas from sources in North America. Helium poses a particular challenge for the gas clean-up process. While helium is showing no specific interaction with the fuel cell catalysts, it dilutes the fuel and enriches at the anode side under recirculating conditions.

When hydrogen is produced via steam methane reforming and subsequent purification via PSA (pressure swing adsorption), removal of non polar inert gasses is most difficult. Therefore, the fuel purification effort is determined by reducing the N2-content to the levels of the fuel specification.

The adsorbents typically used in PSA are interacting strongly with polar molecules such as CO, H2S, NH3 etc. Using gas purification via PSA to a level required to meet the N2-specification will most likely also remove CO and CO2.

Potential formation mechanisms of other trace impurities need to be checked.

Due to pre desulfurization no major problems concerning sulphur are expected. The amount of H2S entering the PSA is very small and is most likely totally adsorbed by the PSA. However, since H2S is strongly adsorbing to Pt-based catalysts a possibility is remaining that single digit ppb-levels of H2S are affecting fuel cell performance when ultra-low Pt-loading is used at the anode side

Due to the polar nature, the PSA unit most likely will also retain the ammonia to a sufficiently low level for use in PEM fuel cells.

When relaxing the inert gas specification, the effectiveness of PSA for the other contaminants needs to be checked.

Autothermal reforming, coal and biomass gasification as well as platforming are producing a synthesis gas of lower hydrogen content than steam methane reforming. In O2 blown autothermal reformers, Ar is becoming the most difficult to remove impurity.

In synthesis gas production from coal gasification again the argon content is most critical. Currently no economically viable gas cleaning process is known to reduce the Ar content to levels specified in the fuel quality standards.

All thermal processes are typically set up centralized in industrial scale.

Hydrogen production from water electrolysis is leading to rather pure hydrogen with the main contaminants being oxygen and water. Oxygen can be removed catalytically. Care has to be taken to remove traces of aerosols. Water electrolysis is a process which can be used centrally and decentralized. The cost of hydrogen is strongly influenced by the electricity cost. Recent studies showed the suitability of hydrogen produced from water electrolysis for use in PEM fuel cells.

By-product hydrogen from chemical processes can be used. Depending on the origin, the gas quality is similar to water electrolysis. However, the amalgam process for chlorine production gives rise to traces of Hg. The effect of the remaining amount of Hg after gas cleaning is currently not known. Corrosion of certain Cu and Al containing materials in the fuel system as well as deactivation of Pt-catalysts might happen.

The table shown in following figure contains values mentioned in the initial guidelines SAE and ISO (ISOTC197WG12, technical specification TS14687-2 approved and published). All limiting values were driven by USA and Japan.

In table 1, impurities marked by a blue arrow are well known to be present in the SYN-Gas used for hydrogen fuel production. Impurities marked in pink are also known to be present, however, the data available on quantities and their relation to process conditions is still limited. Impurities marked in red cannot be ruled out on the basis of the processes used, however, the actual amount and the conditions of impurity formation are not clearly known. This assessment has been obtained for H2 from reforming.

This work allowed the consortium to point out the impurities determining the effort required to clean hydrogen to specification. Inert gasses are of particular concern in this context. The concentrations of other impurities mentioned in the fuel quality standards are not routinely determined analytically. Hydrogen fuel quality assurance via trace analytical methods will affect the hydrogen cost, particularly when expensive state of the art trace analytical methods need to be used.

Impact of impurities depending of PEMFC operation mode:

This task of the project showed that the operation conditions have an important effect on the impact of impurities contained in hydrogen for PEMFC application. Dynamic cycle (including on/off phase) as well as steady state condition has been tested and compared. The main conclusions is that on/off and dynamic cyles with low current stages are beneficial to mitigate the impact of pollutant (especially CO) on the MEA performances.

Thus, under real application, the impact of pollutant, on the anode side, should be less dramatic that the ones oberserved in laboratory tests when steady state currents are applied.

Moreover the recirculation rate of H2 has an important effect on the impurities tolerance and this aspect of the PEMFC stack management could be optimized to mitigate the impact of H2 impurities.

Furthermore, the analytical tools developed by the consortium now allow quantifying the most relevant and challenging impurities in H2 (total sulphur compound and formaldehyde). The limit of quantification for total sulphur compound has reached 3.3 ppb (ISO standard highest acceptable level: 4 ppb). The limit of detection for formaldehyde has reached 5 ppb for formaldehyde and 10 ppb for formic acid which is, for formic acid, at least 20 times less than the highest acceptable level required by ISO.

Potential Impact:

The project has outlined the fact that part of the existing industrial-scale SMR plants is already able to produce hydrogen compatible with the latest ISO/DIS 14687-2 standards at no extra costs. This applies to those SMR plants which are typically employed for non-oil refinery applications, such as higher-quality hydrogen for industrial or chemical applications. Where necessary, hydrogen purification from CO to ISO standards may add around €0.70 Euro per kg of hydrogen.

On the other hand, CO concentration over 2 PPM can increase the stack capital costs for stationary FC systems operated in a static loading mode by over 30% more than systems designed to run on pure hydrogen or increase the fuel consumption by ~10%. CO concentrations above 5 PPM are likely to impair the utilisation even at their beginning of life.

Hydrogen quality analysis has the potential to lead to widely different costs up to over €2/kg-H2. It may add as little as few Eurocents per kg (or less) if the analysis service is commissioned by large-sized refuelling stations (e.g. over 500kg-H2/day) or performed at the production plant or performed infrequently. The frequency with which the analyses are performed is the single most important parameters affecting analysis cost.

These preliminary results therefore suggest that requiring an ISO/DIS 14687-2 -compliant CO concentration in the hydrogen fuel may not lead to any substantial cost penalty to end-users if additional CO purification is required by only a small number of production plants.

Industry and customers will need to agree an affordable Quality Assurance procedure which is sufficiently robust to assure customers on quality. This is most important in the early years when hydrogen demand is low.

List of Websites:

Dr. Pierre-André Jacques,

pierre-andre.jacques@cea.fr