(Invited) Standardizing Experimental Methods and Metrics in the Field of Photoelectrochemical (PEC) Water Splitting

Photoelectrochemistry is a particularly rich field of study that combines principles and concepts from both semiconductor physics as well as electrochemistry.  Although its intellectual depth provides incredible opportunities for technical development, it also presents a steep learning curve for scientists new to this field who wish to leverage PEC in their efforts to advance low-carbon energy conversion research.  As a result, PEC studies are not always performed consistently from one laboratory to the next, limiting the ability to accurately compare results in the literature and amongst researchers.  In order to address this challenge, the U.S. Department of Energy formed the PEC Standards Working Group to identify the most readily accessible experimental methodologies as well as the most meaningful metrics required to advance materials development.  Herein, we discuss the path taken towards establishing benchmarks in PEC water splitting as well as the key concepts and methodologies identified as being the most pertinent within the field.  These include various efficiency definitions in addition to techniques such as illuminated 3- and 2-electrode electrochemical measurements.  Such measurements can elucidate important material properties including band structure and charge transport.  Understanding the advantages and the limitations of these methods is a critical step towards enabling researchers to more accurately evaluate the performance capability of PEC devices and to advance progress in the field.