Prediction of Limits of Solar‐to‐Hydrogen Efficiency from Polarization Curves of the Electrochemical Cells

Abstract

The maximum solar‐to‐hydrogen efficiency (STH) in directly coupled photovoltaic‐assisted water‐splitting systems is achieved when the photovoltaic (PV) and electrochemical (EC) devices are power matched precisely. This matching requires that the polarization curve of the EC device crosses the current–voltage (IV) characteristics of the PV device at its maximum power point (MPP). Conversely, each point on the EC polarization curve can be considered the MPP of a PV device optimally coupled to the EC device. Therefore, at each point on the polarization curve, the minimum PV efficiency and maximum EC efficiency can be calculated for a specific irradiance. The product of both efficiencies generates the STH limit that can be attained at that specific point on the polarization curve. This “reverse analysis,” carried out with elementary math, does not involve any modeling or analysis of PV IV characteristics. Herein, this reverse analysis is described and how it can be used to quantify losses in PV–EC systems and the effect of mutual scaling of PV and EC devices is shown. This method is presented using a NiMo/NiFeOX catalyst pair as an example and was applied to a variety of PV–EC combinations described in the literature.