Efficiency Definitions in the Field of PEC

Abstract

Overall solar-to-hydrogen (STH) efficiency is the most important parameter to characterize a PEC device. In fact, materials systems themselves are effectively defined by their highest-recorded STH efficiency; it is the single value by which all PEC devices can be reliably ranked against one another [1]. Unfortunately, published literature in the area of PEC sometimes contains confusing information regarding efficiency including invalid mathematical expressions for device efficiency, improper experimental methods for obtaining efficiency values, and/or wide-scale reporting of efficiencies other than STH without clear distinction. The first goal of this document is to establish proper definitions and mathematical expressions for device efficiencies. Among these definitions, we identify those that are acceptable for wide-scale benchmarking and reporting (for instance in the form of press releases to mainstream media) as well as those definitions which are helpful for their scientific value in material characterization and diagnostic testing (and suitable for journal publications). Later in this document, we overview the proper experimental procedures as well as common pitfalls that concern each type of efficiency measurement.One of the reasons why so much pluralism exists in describing PEC efficiency is that several different measures of efficiency (g) exist; each has a different place in PEC research. Four primary measures of efficiency will be discussed here, which can be split into the two main categories:• Benchmark efficiency (suitable for mainstream reporting of stand-alone water splitting capability) -solar-to-hydrogen conversion efficiency (STH)

Calculation of the Energy Band Diagram of a Photoelectrochemical Water Splitting Cell

“…electrodes. 28,29 The measurable voltage V r,RHE is indicated in 3a) with an arrow on the energy scale, −qV r,RHE . This is also explained in our previous work.…”

Complex Catalytic Materials Based on the Perovskite-Type Structure for Energy and Environmental Applications

“…STH efficiency gives the overall reaction efficiency of a PEC system used for water splitting reaction under simulated solar illumination and with no external voltage applied. Also, it can be calculated only if the electrodes are immersed in the same electrolyte without other sacrificial reagents [176]. STH efficiency can be calculated using the following formula:…”

“…This formula can be applied for PEC devices working in a three-electrode system which implies the addition of a reference electrode. As in the case of STH efficiency, for the calculation of ABPE efficiency the utilization of sacrificial reagents and chemical bias should be avoided [176].…”

“…It offers the possibility to determine the practical efficiency limits of a material that can be used in PEC systems. It can be determined using the following formula [176]:…”

Affinity-Based Detection of Biomolecules Using Photo-Electrochemical Readout

“…One of the most important parameters for evaluating photoactive materials used in PEC devices is IPCE. IPCE measures the photocurrent collected per incident photon flux as a function of illumination wavelength, which allows researchers to compare the efficiency of the photoactive species at different regions of the electromagnetic spectrum (Chen et al, 2013). IPCE collectively evaluates the optical and electronic properties of materials such as their ability to absorb electromagnetic radiation and transport and collect charged carriers through the PEC cell.…”