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The properties and applications of aniperometric gas sensors are reviewecl. An introductory discussion of the general mechanism o f electrochemical gas reactions atid an outline of the construction of amperometric gas sensors is presented The performance of sensors and the relationship of the sensor's performance to the materials of construction and sensor components are described. The analytical charactcristics of a sensor such as sensitiviv, selectivity, response time and noise are intimately related to the materials chosen for membranes, conductive electrolytes, and active electrocatalysts, as well as the choice o f effective operating conditions. The applications of amperometric gas sensors to specific anaI>rtical problems are discussed in the context of required performance. Finally, this article points out technical gaps and the future direction of amperometric gas sensor research including some potential applications. Keferences that are relevant to the field of amperometric gas sensors are summarized in a table which contains the author's name. the electrochemical reaction, and an exemplary application.

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PoisonsInhibitors Interferents a b s t r a c tThe resistance of several models of catalytic, workfunction-based metal-oxide-semiconductor and electrochemical hydrogen sensors to chemical contaminants such as SO 2, H 2 S, NO 2 and hexamethyldisiloxane (HMDS) has been investigated. These sensor platforms are among the most commonly used for the detection of hydrogen. The evaluation protocols were based on the methods recommended in the ISO 26142:2010 standard. Permanent alteration of the sensor response to the target analyte (H 2 ) following exposure to potential poisons at the concentrations specified in ISO 26142 was rarely observed.Although a shift in the baseline response was often observed during exposure to the potential poisons, only in a few cases did this shift persist after removal of the contaminants.Overall, the resistance of the sensors to poisoning was good. However, a change in sensitivity to hydrogen was observed in the electrochemical platform after exposure to NO 2 and for a catalytic sensor during exposure to SO 2 . The siloxane resistance test prescribed in ISO 26142, based on exposure to 10 ppm HMDS, may possibly not properly reflect sensor robustness to siloxanes. Further evaluation of the resistance of sensors to other Si-based contaminants and other exposure profiles (e.g., concentration, exposure times) is needed.

NOTICEThis report was prepared as an account of work sponsored by an agency of the United States government. Neither the United States government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or any agency thereof. Printed on paper containing at least 50% wastepaper, including 10% post consumer waste.iii Executive SummaryOn June 8, 2011, the U.S. Department of Energy (DOE) and the National Renewable Energy Laboratory (NREL) hosted a hydrogen sensor workshop attended by nearly 40 participants from private organizations, government agencies, and academic institutions. The participants represented a cross section of stakeholders in the hydrogen community, including sensor developers, end users, site safety officials, and code and standard developers. The goals were to identify critical applications for the emerging hydrogen infrastructure that require or would benefit from hydrogen sensors, to assign performance specifications for sensors deployed in each application, and to identify shortcomings or deficiencies (i.e., technical gaps) in the ability of current sensor technology to meet the assigned performance requirements. Current (e.g., onboard sensors for hydrogen forklifts) and emerging (e.g., residential) applications were included.The workshop was structured into two parts. The morning session consisted of topical talks that provided background information about various emerging hydrogen energy applications, the certification and listing processes, and about strategies for sensor deployment. Several critical key application areas were specifically identified, and for each application, breakout groups were formed to identify critical performance metrics, assign values to specifications, and identify shortcomings or deficiencies in current sensors to meet these requirements. Three sequential breakout sessions were held, which allowed workshop attendees to participate and provide input into multiple topical areas. Several breakout groups met in parallel, which restricted the size of each group to eight or fewer participants and enabled open discussions. Each breakout group was chaired by a topic expert. The breakout topics and chairs were: Sensor requirements for each application were defined based on feedback from the breakout groups. Although application specific, many requirement metrics overlap applications. For example, response time is a critical paramet...