BEGIN:VCALENDAR VERSION:2.0 PRODID:-//ZContent.net//ZapCalLib 1.0//EN CALSCALE:GREGORIAN METHOD:PUBLISH BEGIN:VEVENT SUMMARY:Photoelectrochemical water splitting to generate hydrogen fuel: pro cedures to accurately benchmark efficiency and materials improvements for increased solar-to-hydrogen efficiency LOCATION:Chemistry A101 TZID:America/Denver DTSTART:20202001T000000 UID:2026-05-01-01-02-56@natsci.colostate.edu DTSTAMP:20260501T010256 Description:About the Seminar:\nSolar-to-hydrogen (STH) conversion efficien cy a common figure of merit for evaluating and comparing research results\ , and it largely establishes the prospect for successfully introducing com mercial solar water-splitting systems. Present measurement practices do no t follow well-defined standards\, and common methods consistently overesti mate performance. To remedy this need we confirmed underestimated influenc e factors and proposed experimental strategies for improved accuracy[1].Ou r focus was tandem (dual absorber) devices that have the prospect for grea ter STH efficiency[2]\, but increased complexity that requires more carefu l consideration of characterization practices. We performed measurements o n an advanced version of the classical GaInP2/GaAs design[3] while conside ring (i) calibration and adjustment of the light source\, (ii) validation of results by incident photon-to-current efficiency (IPCE)\, and (iii) def inition and confinement of the active area of the device.\nWe initially me asured 21.8% STH efficiency using a tungsten broadband light source\, a ca librated GaInP2 photovoltaic reference cell\, and epoxy-encased photocatho des. In contrast\, integrating experimental IPCE over the AM 1.5G referenc e solar spectrum showed that less than 10% STH conversion is possible. We performed a set of on-sun measurements that gave 16.1% STH efficiency befo re eliminating indirect light coupled to the sample by using a collimating tube and 13.8% STH efficiency. However\, the value still significantly ex ceeded the current density expected according to the quantum efficiency me asured via IPCE. Finally\, suspecting that the illuminated area is poorly defined by epoxy\, we use a compression cell for an epoxy-free area defini tion\, resulting in 9.3% STH efficiency – a number corroborated by our I PCE results.\nIn order to economically generate renewable hydrogen fuel fr om solar energy using immersed semiconductor-based devices\, the U.S. Depa rtment of Energy Fuel Cell Technologies Office has established technical t argets of over 20% STH efficiency with several thousand hours of stability under operating conditions [4]. We had to employ several key solid-state technological advances to achieve STH efficiencies exceeding 16% [5]. The first improvement was to increase the device photocurrent via extending th e infrared absorption using a non-lattice-matched 1.2 eV InGaAs junction\, created by the inverted metamorphic multijunction (IMM) technique develop ed by NREL’s III-V photovoltaics group. The second modification was to a dd a thin n-GaInP2 layer to p-GaInP2 to generate a \"buried junction\"\, w hich increased the open-circuit voltage of the device by several hundred m V and enabled 14% STH efficiency. Finally\, we increased the top junction photon conversion efficiency by adding an AlInP \"window layer\"\, which i s commonly used in solid-state PV devices to reduce surface recombination. Through the use of a collimating tube\, we measured our devices outdoors under direct solar illumination and verified over 16% STH conversion effic iency.\n[1] H. Döscher\, J. L. Young\, J. F. Geisz\, J. A. Turner\, and T. G. Deutsch\, “Solar to hydrogen efficiency: Shining light on phoelect rochemical device performance\,” Energy Environ. Sci. 2015.\n[2] H. Dös cher\, J. F. Geisz\, T. G. Deutsch\, and J. A. Turner\, “Sunlight absorp tion in water – efficiency and design implications for photoelectrochemi cal devices\,” Energy Environ. Sci. 2014.\n[3] O. Khaselev and J. A. Tur ner\, “A Monolithic Photovoltaic-Photoelectrochemical Device for Hydroge n Production via Water Splitting\,” Science. 1998.\n[4] http://energy.go v/sites/prod/files/2015/06/f23/fcto_myrdd_production.pdf\n[5] James L. You ng\, Myles A. Steiner\, Henning Döscher\, Ryan M. France\, John A. Turner \, and Todd G. Deutsch\, “Direct solar-to-hydrogen conversion via invert ed metamorphic multi-junction semiconductor architectures” Nature Energy 2\, 17028 (2017).\n \;\nAbout the Speaker:\nSenior Scientist\, Chemis try and Nanoscience Center\nTodd Deutsch has been studying photoelectroche mical water splitting since interning in Dr. John A. Turner’s lab at NRE L in 1999. He performed his graduate studies on III-V semiconductor water- splitting systems under the joint guidance of Dr. Turner and Prof. Carl A. Koval in the Chemistry department at the University of Colorado-Boulder. Todd officially joined NREL as a postdoctoral scholar in Dr. Turner’s gr oup in 2006 and became a staff scientist two years later. Since 2014\, he has led NREL’s applied water splitting program that aims to identify and characterize appropriate materials for economically generating hydrogen f uel from water using sunlight as the only energy input. His work has focus ed on inverted metamorphic multijunction III-V semiconductors and corrosio n remediation strategies for high-efficiency water-splitting photoelectrod es. Recently\, Todd has ventured into new research areas as the principal investigator for projects that seek to develop advanced bipolar membranes for reversible fuel cells and CO2 electrolyzers. The CO2 electrolyzer proj ect is a multi-lab program that aims to invent CO2 electrolyzers that can electrocatalytically reduce CO2 to useful chemicals and fuels at industria lly-relevant rates. Todd has been honored as an Outstanding Mentor by the United States Department of Energy\, Office of Science nine times in recog nition of his work as an advisor to over thirty students in the Science Un dergraduate Laboratory Internship program at NREL.\nHe has over 40 peer-re viewed publications that have garnered over 4500 citations and he has give n over 35 invited presentations and seminars. Todd received a B.S. in Chem istry\, cum laude\, from Humboldt State University and a Ph.D. in Analytic al Chemistry from the University of Colorado-Boulder.\n\n 4:00 pm END:VEVENT END:VCALENDAR