Three terminal photoelectrodes to enable light-driven fuel production under variable and diurnal condition

To achieve practical applications, photoelectrochemical (PEC) fuel-forming systems must be able to maintain stability throughout the entire diurnal illumination cycle. This requires a fundamental redesign of the standard photoelectrode architecture used for PEC reactions. Within the Liquid Sunlight Alliance Solar Fuels Hub, we have adapted advanced photovoltaic technologies for PEC applications to create multiple types of new fuel-forming systems. In this talk, I will discuss (1) the use of interdigitated back contact architectures to enhance device stability under diurnal (day/night) cycling, and (2) approaches to integrating multiple catalytic microenvironments in a single photoelectrochemical device.

1) Three terminal (3T) photocathodes with interdigitated back contacts can overcome the limitations of traditional two terminal photoelectrodes by adding an extra electrical contact. This contact provides a low resistance path for both photoelectrochemical and electrochemical (i.e., non-light-driven) reactions on the same electrode. The 3T design offers benefits like cathodic protection and in-situ switching between operational modes. I will demonstrate that 3T-based Si photocathodes maintain PEC activity after several hours of light/dark cycling in aqueous electrolyte, and how this architecture can integrate into tandem PEC systems [1].

2) We have adapted the design of III-V photovoltaic devices to function as cascade PEC electrodes that create multiple local catalytic microenvironments on the same photoelectrode. These 3TT devices can have two distinct catalyst sites operating at different voltages when illuminated, enabling them to drive cascade reactions. Modeling indicates the potential advantages of these 3TT devices over traditional two-terminal, two-junction devices, particularly in terms of spectral tolerance and formation of multi-carbon products. We have demonstrated cascade reactions that can drive the valorization of CO₂ to methanol using our 3TT photoelectrodes coupled to cobalt phthalocyanine [2]. Research is ongoing to understand how these devices perform under diurnal illumination conditions to better understand how product distributions change with varying conditions.