Ten-percent solar-to-fuel conversion with nonprecious materials

Abstract

Direct solar-to-fuels conversion can be achieved by coupling a photovoltaic device with water-splitting catalysts. We demonstrate that a solar-to-fuels efficiency (SFE) > 10% can be achieved with nonprecious, low-cost, and commercially ready materials. We present a systems design of a modular photovoltaic (PV)-electrochemical device comprising a crystalline silicon PV minimodule and lowcost hydrogen-evolution reaction and oxygen-evolution reaction catalysts, without power electronics. This approach allows for facile optimization en route to addressing lower-cost devices relying on crystalline silicon at high SFEs for direct solar-to-fuels conversion.istributed and grid-scale adoption of nondispatchable, intermittent, renewable-energy sources requires new technologies that simultaneously address energy conversion and storage challenges (1, 2). Coupling photovoltaics to drive catalytic fuelforming reaction, such as water splitting to generate H 2 , allows for direct solar-to-fuels conversion. The solar-generated H 2 can effectively be harnessed to electricity by fuel cell devices (3, 4) or converted to liquid fuels upon its combination with CO or CO 2 (5-7). For this technology to be effectively implemented, a solar-to-fuels conversion efficiency (SFE) of 10% or higher is desirable (8, 9).Direct photoelectrochemical (PEC) water splitting by a single absorber material has attracted a vast amount of attention (10, 11), and recent progress indicates improvements in the field (12, 13); but after decades of research, direct PEC faces three challenges to increase conversion efficiency: (i) Direct absorber band alignment is required to provide carriers with appropriate potential to both half reactions. Although such an alignment is difficult to achieve in a single material initially, any change in band alignment due to changing surface conditions can result in further efficiency degradation. This makes it challenging to design devices that maintain robust, high efficiencies in actual operation.(ii) The wide absorber bandgap (>1.23 eV; typically >1.6 eV) needed to drive the water-splitting reaction is not optimized for the solar spectrum, which results in a maximum SFE of only 7% (14-16). (iii) The absorbers are poor catalysts, and they are incapable of efficiently performing the four proton-coupled electron transfer chemistry (17-22) that is needed for water splitting.These deficiencies can be overcome by substituting a PEC device with a buried-junction photovoltaic (PV) device and an electrochemical catalyst (EC) system, forming a PV-EC tandem (23-27). In a buried-junction device, the electric field is generated at an internal junction within the semiconductor and is then coupled with water-splitting catalysts through ohmic contacts, which can either be conductive coatings directly deposited onto the PV or connected through wires to the electrodes. The buried junction relaxes the constraints imposed by a PEC device because it separates light absorption from catalysis, and does not require that the absorber be stable in ...

CO2 Reduction: From the Electrochemical to Photochemical Approach

“…The ideal limiting SFE at a single absorber particle is η = 14.4% based on a light absorber with a 2.0 eV band gap 42. It is suggested that a >10% SFE is required for photocatalysis to be an economically viable resource 43, 44 …”

Experimental demonstrations of spontaneous, solar-driven photoelectrochemical water splitting

“…[50][51][52]84 More recently, materials such as CIGS and halide perovskite-based cells have been adapted into PEC cells that exceeded 10% STH efficiency. [62][63][64] Over the last decade, materials such as metal oxides, which have been developed specifically for PEC applications, have seen substantial research interest and progress. Reported STH efficiencies for devices containing metal-oxide-based active components now exceed 5%.…”

An Integrated Device View on Photo-Electrochemical Solar-Hydrogen Generation

“…Laboratory-scale demonstrations of these systems have achieved remarkable performances. Systems based on III-V semiconductors have been developed and show efficiencies up to 18% STH using concentrated solar irradiation (19,35), whereas systems based on Si PV cells have achieved efficiencies above 10% (86)(87)(88)(89)(90)91). More recently, solution-processed perovskite-based PV components together with earth-abundant electrocatalysts have been used to drive the watersplitting reaction at high efficiency levels, up to 12.3% STH (92) (Figure 3c).…”