DOCSLIB.ORG

Pathways to Commercial Success: Technologies and Products Supported by the Hydrogen, Fuel Cells & Infrastructure Technologies Program

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Pathways to Commercial Success: Technologies and Products Supported by the Hydrogen, Fuel Cells & Infrastructure Technologies Program HYDROGEN, FUEL CELLS & INFRASTRUCTURE TECHNOLOGIES (HFCIT) PROGRAM Pathways to Commercial Success: Technologies and Products Supported by the Hydrogen, Fuel Cells & Infrastructure Technologies Program August 2009 Prepared by Pacific Northwest National Laboratory for the U.S. Department of Energy Hydrogen, Fuel Cells & Infrastructure Technologies Program Table of Contents Summary .................................................................................................................................................................................................................. v 1.0 Introduction.......................................................................................................................................................................................................1-1 1.1 A Brief History of HFCIT........................................................................................................................................................................1-1 1.2 Organization of the HFCIT Program....................................................................................................................................................1-2 1.3 Contents of this Report............................................................................................................................................................................1-4 2.0 Approach...........................................................................................................................................................................................................2-1 2.1 Patent Search and Analysis.....................................................................................................................................................................2-1 2.2 Technology Tracking to Identify and Describe Commercial and Emerging Technologies........................................................2-3 3.0 Results ..............................................................................................................................................................................................................3-1 3.1 Patent Search and Analysis.....................................................................................................................................................................3-1 3.2 Commercial and Emerging Technology Identification and Tracking Results...............................................................................3-3 Appendix A: Technology Tracking List..............................................................................................................................................................................................A-1 Appendix B: Technology Tracking Data Collection Template.......................................................................................................................................................B-1 Appendix C: Patent Status List.............................................................................................................................................................................................................C-1 Appendix D: Commercial Technology Descriptions.......................................................................................................................................................................D-1 Appendix E: Emerging Technology Descriptions............................................................................................................................................................................E-1 iii Summary The Hydrogen, Fuel Cells & Infrastructure Technologies (HFCIT) Program integrates activities in hydrogen production, delivery, and storage with transportation and stationary fuel cell activities, in addition to crosscutting efforts in technology validation; safety, codes, and standards; education; manufacturing research and development; and market transformation. The Program office consolidated efforts within the U.S. Department of Energy’s (DOE’s) Office of Energy Efficiency and Renewable Energy (EERE) in the 2002 time frame. The HFCIT Program and the predecessor programs that were consolidated have been conducting a wide range of hydrogen and fuel cell research and development projects, some of which have resulted in products and technologies now available in the commercial marketplace. The purpose of the project described in this report was to identify and document the commercial and near-commercial (emerging) hydrogen and fuel cell technologies and products that benefited from EERE support. To do this, Pacific Northwest National Laboratory (PNNL) undertook two efforts simultaneously. The first effort was a patent search and analysis to identify hydrogen- and fuel-cell-related patents that are associated with HFCIT-funded projects (or projects conducted by DOE-EERE predecessor programs) and to ascertain the patents’ current status, as well as any commercial products that may have used the technology documented in the patent. This patent analysis identified 144 patents associated with research supported by HFCIT, out of approximately 360 potential HFCIT patents, dating back to 1977, that were found in the original patent search. The 144 HFCIT patents include: 74 fuel cell patents, 49 production/delivery patents, and 21 storage patents. More than 70 of these patents were issued after 2002. Three types of organizations received the patents: national laboratories (69 patents), private companies (56 patents), and universities (19 patents). The national laboratories had patent awards for fuel cell and production/ delivery technologies that were almost equal to those awarded to private companies in these two areas. The national laboratories had 62% of the awards in the storage area. While the universities received fewer total patent awards, they had 74% of their patents in the production/delivery area. The national laboratories and private companies both received more than half of their patents in the fuel cell area. The patent award status by use indicated that 3 patents are currently used in commercial products and 18 are part of research now taking place on emerging technologies. In addition, 51 awarded patents are still being used in research that is more than 3 years from a commercial product and the status of one patent is still unverified. Of the patents reviewed, 50% are no longer being used in research. This was particularly true in the fuel cell area, where 44 of the 73 patents (60%) are no longer being used in research. However, this is not true in the storage or production/delivery area, where most of the patents are still being used in research. The second effort was a series of interviews with current and past HFCIT personnel, a review of Hydrogen Program annual reports, and an examination of hydrogen- and fuel-cell-related grants made under the Small Business Innovation Research and Small Business Technology Transfer Programs, and within the HFCIT portfolio. This effort identified 22 commercial technologies including three using patents identified in the first effort. From 2000 – 2006, one to three commercial technologies entered the market per year. In 2007, five technologies entered the market, and in 2008, six technologies did so. This effort identified 47 emerging technologies. An almost equal number of emerging technologies occurred between the fuel cell and production/delivery areas, with the storage area having far fewer emerging technologies. This report documents the details of this study including the specific patents as well as commercial and emerging technologies that resulted from the HFCIT Program. v 1.0 Introduction This report documents the results of an effort to identify and characterize commercial and near-commercial (emerging)1 technologies and products that benefited from the support of the Hydrogen, Fuel Cells & Infrastructure Technologies (HFCIT) Program and its predecessor programs within the U.S. Department of Energy’s (DOE’s) Office of Energy Efficiency and Renewable Energy (EERE). The effort was undertaken to meet the following primary objective: To identify and characterize commercial and near-commercial (emerging) technologies that benefited from support of the HFCIT Program and its predecessor programs within DOE’s EERE. Commercialization of technologies that were cultivated in a government research and development (R&D) program is generally viewed as a measure of success. However, in addition to developing this indicator of the general success of the HFCIT’s R&D program, by studying the commercial successes documented in this report, the reader may gain insight into pathways for more widespread introduction of hydrogen and fuel cell technologies. With the tracking of commercialization successes, HFCIT is likely to more effectively manage its R&D programs, repeat successful approaches to commercialization, and learn from unsuccessful pathways. PNNL has been conducting similar technology tracking activity for the EERE Industrial Technologies Program (and its predecessors) for over two decades and agreed to develop a similar methodology and undertake the commercial technology tracking project for hydrogen and fuel cells. The results presented in this report represent the findings from the first stage of the PNNL effort. The information presented on commercial and emerging technologies fulfills the primary objective – to assess the commercialization status of EERE-developed hydrogen
Load more

Recommended publications
  • Gas Detection Products Ammonia & Other Gases
    Gas Detection Products Ammonia & Other Gases Product Catalog 2021 Table of Contents Price List .......................................................................................................................................................................................... 4-31 Controllers ....................................................................................................................................................................................... 32-39 GG-6 ....................................................................................................................................................................................... 32-33 GG-6 Remote Display ........................................................................................................................................................... 34-35 GG-2 ....................................................................................................................................................................................... 36-37 EM2 Entrance Monitor ......................................................................................................................................................... 38-39 Ammonia Sensors ............................................................................................................................................................................. 40-49 GG-NH3 .................................................................................................................................................................................
    [Show full text]
  • Gas Purifiers and Traps
    gas chromatography Gas Purifiers and Traps Why Use Gas Purifiers? Choosing the Right Gas Purifier for Your Application A clean gas stream helps guarantee the quality of your GC analysis and the reliability of your results. It also helps prolong There are a variety of gas purifiers available. Some remove column life and minimize detector noise. Gas purifiers act a specific contaminant while others remove multiple as an insurance policy, protecting your instrumentation and contaminants from your gas stream. There are several analytical columns from these contaminants. They will not factors you need to consider when selecting purifiers for your however, convert low purity gas into ultra high purity gas. application. These include contaminants potentially present in Grace carries a variety of gas purifiers in two different styles. your gas stream, gas purity levels required, flow and pressure See Table 1 for details. limitations, space availability, and desired convenience when replacing spent traps. Moisture, hydrocarbon, and oxygen traps are the most commonly used purifiers for GC applications. Moisture traps are typically packed with molecular sieves. After extensive heating, these crystalline structures lose their water of hydration opening a cavity that is readily filled with any compound that can fit. Water fits perfectly. However, it will also remove HCl, CO2, SO2, Cl2, or any gas with an effective diameter smaller than water. Hydrocarbon traps are packed with an activated charcoal that adsorbs any organic compound larger than methane. Size and molecular weight of the organic contaminants will greatly effect the capacity of the trap, and to a smaller degree, trap 5334 5335 efficiency.
    [Show full text]
  • Testing the Performance of Hydrogen Sensors
    Testing the Performance of Hydrogen Sensors Nathan D. Marsh National Institute of Standards and Technology, Gaithersburg, MD USA Thomas G. Cleary National Institute of Standards and Technology, Gaithersburg, MD USA Abstract The acceptance of hydrogen as a widely-available energy source will depend to some extent on the perceived and actual safe dispensing and storage of hydrogen by the general public. Reliable detection of an accidental hydrogen gas release and mitigation of the hazard through designed safety systems is a key component of hydrogen powered systems in commercial, residential, and transportation uses. In anticipation of this emerging market, inexpensive hydrogen gas sensors based on a range of sensing technologies are becoming increasingly available. We have developed a new bench-scale test apparatus for hydrogen sensor performance, the Hydrogen Detector Environment Evaluator (HyDEE), based on our previous experience with hydrogen sensors in a small flow cell and in the Fire Emulator / Detector Evaluator. In particular, we have found that dynamic changes are relevant to hydrogen sensor performance, as they affect both response rate of the sensor and are also necessary to return the sensor environment to its baseline state. The ability to induce dynamic changes is most easily accomplished with a flow system similar to a small wind tunnel. In this system, we can expose sensors to hydrogen and other gases (particularly hydrocarbons, which many hydrogen sensors are also sensitive to) as well as humidity and changes in temperature. Improvements over the previous exploratory tests include substantially reduced volume allowing higher gas concentrations, and the ability to cool the system as well as heat it, in order to achieve a wider dynamic range in temperature and to more accurately simulate the environments to which sensors may be exposed in the real world.
    [Show full text]
  • Gas Purification
    GAS PURIFICATION Overview Overview Gas purity is essential in any application requiring extreme sensitivity. Contaminant traps Gas specific purifiers and gas purifiers for specific gases dramatically reduce the levels of contaminants, enhance the purity of lower grade helium, and help ensure instrument stability, reproducibility, and lower maintenance costs. Specialized purifiers Purifiers for specific gases Specialized purifiers Contaminant traps Purifiers from VICI We also offer purifiers for special Metronics are applications, such as chemical ionizatin designed to go in- MS, and nitrogen for LC/MS or from a line with the carrier nitrogen generator. Our liquid carbon or detector gas dioxide purification technology can result supply. These include in significant cost savings. models which were original equipment gas purifiers for the ● For nitrogen for LC/MS Agilent Mass Spec and LC Mass Spec. ● For nitrogen generators Also available are VICI Valco ● For chemical ionizatin MS heated helium and nitrogen purifiers, for peak purification ● For liquid carbon dioxide performance. ● Heated helium purifiers ● Air ● Heated nitrogen purifiers ● Carbon dioxide ● Helium ● Hydrogen ● Methane ● Nitrogen Website : www.chromtech.net.ay E-mail : [email protected] TelNo : 03 9762 2034 . in AUSTRALIA Contaminant traps For applications with a single contaminant of interest, high capacity contaminant specific traps are your best option, since they generally have four times as much capacity for the specific contaminant as a gas specific purifier. ●
    [Show full text]
  • 1 Nanocomposite Nio:Au Hydrogen Sensors with High Sensitivity And
    Nanocomposite NiO:Au hydrogen sensors with high sensitivity and low operating temperature M. Kandylaa*, C. Chatzimanolis-Moustakasa,b, E.P. Koumoulosb, C. Charitidisb, and M. Kompitsasa aNational Hellenic Research Foundation, Theoretical and Physical Chemistry Institute, 48 Vasileos Constantinou Avenue, 11635 Athens, Greece bNational Technical University of Athens, School of Chemical Engineering, 9 Heroon Polytechniou Street, 15780 Zografou, Greece Abstract We present results on the development of nanocomposite NiO:Au thin-film hydrogen sensors, which are able to detect hydrogen concentrations as low as 2 ppm in air, operating at low temperatures in the range 125 – 150oC. Thin NiO films were sputter- deposited on oxidized silicon substrates. The structural, morphological, and nanomechanical properties of the films were investigated with respect to post- deposition annealing. Au nanoparticles were added on the NiO surface via pulsed laser deposition and the films were tested as hydrogen sensors before and after Au deposition. The performance of the NiO films as hydrogen sensors improved significantly in the presence of Au nanoparticles on the surface. The detection limit (lowest detectable hydrogen concentration) decreased by two orders of magnitude, while the response time also decreased by a factor of three. KEYWORDS: A. composites, A. oxides, B. sputtering, B. laser deposition, D. electrochemical properties * Corresponding author: 1 M. Kandyla National Hellenic Research Foundation Theoretical and Physical Chemistry Institute 48 Vasileos Constantinou Avenue 11635 Athens, Greece Tel.: +30 210 7273826, Fax: +30 210 7273794 E-mail: [email protected] 2 1. Introduction Hydrogen is widely used in the chemical, petroleum, and metallurgical industries, as well as in power station cooling.
    [Show full text]
  • Hydrogen Sensor Specifications
    Control Instruments Corporation Product Specifications 25 Law Drive, Fairfield, NJ 07004-3295 USA Hydrogen Sensor for SmartMaxII Telephone 973-575-9114 Fax 973-575-0013 Email: [email protected] Internet: www.controlinstruments.com Sensor Design The Hydrogen Sensor employs electrochemical 9.375 inches technology. The sample diffuses into a micro fuel cell, where it chemically reacts to produce an electrical current. The micro fuel cell is designed so that the current produced is 3.625 inches proportional to the concentration of hydrogen present. The signal is then amplified into a mA output. The output signal is linear and readings are displayed in parts per million Cell Housing concentrations. Calibration Port Junction Box Construction Standard Specifications The sensor assembly consists of the micro fuel cell which Part Number SNR476 plugs into the electronics. The cell and electronics are Standard Range 0-1000 Parts Per Million (PPM) housed in an aluminum sensor body which connects to a Optional Range 0-2000 PPM junction box for field wiring. A collar protects the sensor Accuracy ± 5 PPM from environmental conditions and also provides a means of Response Time 40 seconds to 50% of scale introducing calibration test gas. Repeatability ± 1% full scale The micro fuel cell employs a capillary diffusion barrier Drift ± 2% full scale per month which eliminates the possibility of puncturing the membrane Assembly Rating Class 1, Division 1 and destroying the cell. The cell is a rugged and stable Assembly Material Aluminum design that is less sensitive to temperature and pressure Operating Life 2 years variations than other electrochemical cells. Storage life in container 6 months An on-board heater protects the cell and extends its Temperature Limits -20°C (-4°F) to 50°C (122°F) useful operating range in sub-freezing temperatures.
    [Show full text]
  • High-Sensitivity and Low-Power Flexible Schottky Hydrogen Sensor Based on Silicon Nanomembrane
    Poster Session II: IoT Including Nanosensors High-sensitivity and Low-power Flexible Schottky Hydrogen Sensor based on Silicon Nanomembrane Minkyu Cho Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology (KAIST) . Hydrogen (H2) is useful as a future clean energy resource and an ideal replacement for fossil fuel . Various applications such as hydrogen vehicle, petroleum refining, glass purification, semiconductor manufacturing etc. H2 is flammable at concentrations over 4% by volume, therefore high sensitivity H2 sensor with fast response time is necessary . Silicon nanomembrane based diode type H2 sensor was demonstrated exhibiting high sensitivity and low power consumption Source:http://www.hydrogen.energy.gov/systems_integration.html US Department of energy High Mobility Advantages of Si • Well established processing technique Graphene -> more freedom in sensor design Carbon Nanotubes GaAs, GaN Low flexible rigidity of thin Si *Si Poly-Si a-Si Polymers Good material candidate for Low Mobility high performance flexible/wearable H2sensors . The operation principle of the sensor is based on Schottky barrier lowering effect upon exposure to H2 . H2 gas molecules are diffused into Pd layer forming Palladium Hydride (PdHx) at Pd/Si interfaces . Device simulations show that effective current quenching has been occurred in 50 nm thickness SiNM H2 lowering standby power consumption of the sensor Reduced Si thickness Low standby power consumption Excellent mechanical properties o Low thermal budget (< 110 C) Applicable to wafer-scale process . High Sensitivity ( > 700% @ 0.5% H2 concentration) and Fast Response Time (τ10−90= 22s) . Good Linearity (R2 > 0.98) and Low Limit of Detection (50 ppm, limited by MFC) . Minor Increased Sensitivity under Tensile Strain (Piezoresistive property of SiNM) .
    [Show full text]
  • Hydrogen Gas Sensors Based on Semiconductor Oxide Nanostructures
    Sensors 2012, 12, 5517-5550; doi:10.3390/s120505517 OPEN ACCESS sensors ISSN 1424-8220 www.mdpi.com/journal/sensors Review Hydrogen Gas Sensors Based on Semiconductor Oxide Nanostructures Haoshuang Gu *, Zhao Wang and Yongming Hu Faculty of Physics and Electronic Technology, Hubei University, Wuhan 430062, China; E-Mails: [email protected] (Z.W.); [email protected] (Y.H.) * Author to whom correspondence should be addressed; E-Mail: [email protected]; Tel.: +86-027-8866-5568; Fax: +86-027-8866-3390. Received: 8 March 2012; in revised form: 1 April 2012 / Accepted: 25 April 2012 / Published: 30 April 2012 Abstract: Recently, the hydrogen gas sensing properties of semiconductor oxide (SMO) nanostructures have been widely investigated. In this article, we provide a comprehensive review of the research progress in the last five years concerning hydrogen gas sensors based on SMO thin film and one-dimensional (1D) nanostructures. The hydrogen sensing mechanism of SMO nanostructures and some critical issues are discussed. Doping, noble metal-decoration, heterojunctions and size reduction have been investigated and proved to be effective methods for improving the sensing performance of SMO thin films and 1D nanostructures. The effect on the hydrogen response of SMO thin films and 1D nanostructures of grain boundary and crystal orientation, as well as the sensor architecture, including electrode size and nanojunctions have also been studied. Finally, we also discuss some challenges for the future applications of SMO nanostructured hydrogen sensors. Keywords: hydrogen gas sensor; semiconductor oxides; nanostructure; thin films; one-dimensional nanostructures 1. Introduction Hydrogen is regarded as one of the best clean energy carriers, which is the ultimate fossil fuel candidate, with a high heat of combustion (142 kJ/g), low minimum ignition energy (0.017 mJ) and wide flammable range (4–75%), as well as high burning velocity.
    [Show full text]
  • Comparison of Available Portable Combustible Gas and Hydrogen Sensors
    Comparison of Available Portable Combustible Gas and Hydrogen Sensors June 2011 FOREWORD This report documents a comparison of currently commercially available portable equipment that can be used to sense/detect the presence of hydrogen and/or combustible gases in the air. Available devices, identified via a literature search, were compared and ranked based on a common set of ranking criteria and an objective rating system for each criterion. The devices were rated against each criterion based on data contained in manufacturer literature. This document is intended as a reference for the Federal Motor Carrier Safety Administration in evaluating available equipment that might be used by agency inspectors to search for fuel leaks from commercial vehicles powered by hydrogen. In the context of this report, the presence of hydrogen detected in a concentration greater than 25 percent of the lower flammable limit (LFL) of hydrogen in the air would be considered a leak. Such a search would most likely be done in the context of a roadside vehicle inspection conducted in accordance with the North American Standard Inspection Procedures. In accordance with current inspection procedures, a fuel leak would be grounds to declare a vehicle out of service for a safety violation. Given that hydrogen is a colorless, odorless gas, it is unlikely that any vehicle inspector could identify a small leak (as defined above) from a hydrogen fuel system without the aid of detection equipment. NOTICE This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The United States Government assumes no liability for its contents or the use thereof.
    [Show full text]
  • Trends in Gas Sensor Development for Hydrogen Safety
    TRENDS IN GAS SENSOR DEVELOPMENT FOR HYDROGEN SAFETY Hübert, T. 1, Boon-Brett, L. 2, Palmisano, V. 2, Frigo, G. 3, Hellstrand, Å. 3, Kiesewetter, O. and May, M. 4 1 BAM Bundesanstalt für Materialforschung und -prüfung, Unter den Eichen 87, 12205 Berlin, Germany, [email protected] 2 European Commission – Joint Research Centre (JRC) Institute for Energy and Transport, Westerduinweg 3, (P.O.Box 2), 1755 ZG Petten, The Netherlands, [email protected] 3 Sensitron S.r.J., Viale della Republica 48, I-20010 Comaredo, Italy, [email protected] 4 UST Umweltsensortechnik GmbH, Dieselstraße 2, D-98716 Geschwenda, Germany, [email protected] Abstract Gas sensors are applied for facilitating the safe use of hydrogen in, for example, fuel cell and hydrogen fuelled vehicles. New sensor developments, aimed at meeting the increasingly stringent performance requirements in emerging applications are presented based on in-house technical developments and a literature study. The strategy of combining different detection principles, i.e. sensors based on electrochemical cells, semiconductors or field effects in combination with thermal conductivity sensor or catalytic combustion elements, in one new measuring system is reported. This extends the dynamic measuring range of the sensor while improving sensor reliability to achieve higher safety integrity through diverse redundancy. The application of new nanoscaled materials, nano wires, carbon tubes and graphene as well as the improvements in electronic components of field- effect, resistive-type and optical systems are evaluated in view of key operating parameters such as sensor response time, low energy consumption and low working temperature. 1.0 INTRODUCTION Fuel cell systems, usually consisting of gas preparation and supply modules, pipes, connections, valves as well as a fuel cell stack, are susceptible to hydrogen leakages.
    [Show full text]
  • Application of Nanotechnogy on Hydrogen Production and Storage
    The 21st Century Frontier 과학기술부 21세기 프론티어연구개발사업 21st Century Frontier R&D Program APPLICATIONAPPLICATION OFOF NANOTECHNOGYNANOTECHNOGY ONON HYDROGENHYDROGEN PRODUCTIONPRODUCTION ANDAND STORAGESTORAGE ININ KOREAKOREA April 26~27, 2007 Jong Won Kim Director Hydrogen Energy R&D Center http://www.h2.re.kr 4th US-Korea NanoForum, Honolulu, USA, April 26-27, 2007 1 th 4수소에너지사업단US-Korea NanoForum, 업무보고 Honolulu,, 2004.7.9 USA, April 26-27, 2007 Hydrogen Energy R&D Center 1 The 21st Century Frontier Outline I. Hydrogen Economy- Vision II. Technical barrier III. Current R&D activities related to nanotechnology IV. Conclusions 4th US-Korea NanoForum, Honolulu, USA, April 26-27, 2007 2 th 4수소에너지사업단US-Korea NanoForum, 업무보고 Honolulu,, 2004.7.9 USA, April 26-27, 2007 Hydrogen Energy R&D Center 2 The 21st Century Frontier 1. Hydrogen economy-vision Hydrogen Economy Nuclear Hydrogen storage/transportation/distribution Ship Water Electrolysis Wind Infrastructure Bus Solar Photochemical/ Vehicle Thermochemical/ Biological H2 Production Biomass Distributed Power Residential Mobile Submarine 3 th 4수소에너지사업단US-Korea NanoForum, 업무보고 Honolulu,, 2004.7.9 USA, April 26-27, 2007 Hydrogen Energy R&D Center 3 The 21st Century Frontier 2. Technical barriers Production/ Amounts Utilization Utilization *Oil refinery (desulfurising, reforming) ~ 1% TPES *Chem.Ind.: Ammonia, fertilizer, methanol (Total Primary *Metal Industry *Food( Fat, oil) *welding *Electronics Energy supply) *cryogenic *Electric generator-cooling Raw materials User ~95% fossil fuel (NG etc) About 50million tons ~ 45% petroleum ~40% Chem. Ind. ~ 5% electrolysis ~15% others <35% sales >65% self-consumption DomesticDomestic 0.970.97 millionmillion tonton TradeTrade 4848 thousandthousand ton*ton* * Source: Bongjin Kim et al: “The status of domestic hydrogen production, consumption and distribution”, Trans.
    [Show full text]
  • Electrodes for Semiconductor Gas Sensors
    sensors Review Electrodes for Semiconductor Gas Sensors Sung Pil Lee Department of Electronic Engineering, Kyungnam University, 7 Kyungnamdaehak-ro, Masanhappo-gu, Changwon 51767, Korea; [email protected] Academic Editor: Giovanni Neri Received: 7 February 2017; Accepted: 22 March 2017; Published: 25 March 2017 Abstract: The electrodes of semiconductor gas sensors are important in characterizing sensors based on their sensitivity, selectivity, reversibility, response time, and long-term stability. The types and materials of electrodes used for semiconductor gas sensors are analyzed. In addition, the effect of interfacial zones and surface states of electrode–semiconductor interfaces on their characteristics is studied. This study describes that the gas interaction mechanism of the electrode–semiconductor interfaces should take into account the interfacial zone, surface states, image force, and tunneling effect. Keywords: electrodes; semiconductor gas sensors; electrode materials; interfacial layer; transport mechanism 1. Introduction There is a growing demand for gas sensors for efficient use of energy and raw materials, as well as to reduce environmental pollution despite increasingly complex manufacturing processes. The Taguchi sensor that detects reducing gases is the most well-known gas sensor [1], whereas an oxygen sensor based on an ion-conducting sensor is the second most famous type [2–5]. Research and development for gas sensors is conducted in two stages. The first stage is to develop a new sensor whose application is empirically optimized. The characteristics of sensitivity, selectivity, long-term drift, and reliability are defined though its operation mechanism, which is often not fully understood at that stage [6–10]. The second stage is to modify, optimize, and standardize the developed sensor system [11–14].
    [Show full text]