Our recent article in Nature Energy is our first attempt at the development of a scalable photoelectrochemical (PEC) system to produce green hydrogen (H2). Based on our previous critical review article, there are challenges associated with practical solar H2 production. We also found that a minimum of 10% efficiency is required to develop a viable practical PEC system, for which selecting the efficient material is the first criterion. So far metal oxides have been studied for photocatalysis but are far away from such practical efficiency limits. On the other hand, photovoltaic (PV grade) materials (silicon, perovskites, chalcogenides, III-V class) are well established in solar cell industries. Such efficient, scalable PV grade materials could be an option but very few fulfil the requirements for efficient PEC applications, while other materials are efficient but cannot fulfil major criteria including efficiency, low cost, and integration of catalysts.
MHP materials have excellent optoelectronic properties and a tunable band-gap which are desired in the PEC field; e.g. metal-halide perovskites (MHP) can provide the necessary photocurrent and photovoltage to split water and produce oxygen and H2 in a single PEC cell. Such MHP materials can be fabricated at a large area including mini-modules and modules scales. We know that there was only one challenge associated with these materials which was the degradation of MHP in humid conditions because PEC reactions were to be conducted in liquid electrolytes. So, we had to focus on stabilizing such materials using metal-encapsulation for PEC reactions. With such concepts in mind, we selected the stabilized MHP material to apply in the PEC field.
The advantage of our system is integrating multi components in a single PEC device, minimizing the system’s complexity and reducing costs
In the Nature Energy article, we selected the efficient material (e.g. FAPbI3 as MHP) and presented the material & thin-film analyses, with its application as efficient photoelectrodes in PEC water splitting with at least 10% efficiency, which were the primary objectives. After successful experimental results, we achieved the 9.89% efficiency at small-area devices as preliminary results. Such results motivated us to check the efficacy of large-area PEC devices.
Our all-perovskite PEC system is composed of a FAPbI3 photoanode, which has MHP thin films protected using Nickel (25-30 micron thick) metal foil as encapsulation and NiFeOOH as a catalyst layer on it. We optimized this photoanode using different metal foils and studied the in-depth catalyst-electrolyte interactions. Small area FAPbI3 photoanodes (0.25 cm2) were tested using a photoanode connected to a solar cell (PEC-PV) in the single reactor system. As per our preliminary results, we found 9.89% (close to 10%) efficiency using small-area devices. This is because two semiconductor devices are necessary to generate a maximum 2 voltage required for water splitting in O2 and H2 gas. However, the PV component must be kept outside the reactor in the PEC-PV system. To minimize the system complexity, we decided to integrate both components in a single PEC device which avoided the extra use of PV components. This is a unique advantage of our system, and it can reduce the cost of the system.
Main findings for practical applications
As stated above, the unique advantage of our system is integrating multi components in a single PEC device avoiding extra use of PV components which minimize the system’s complexity and reduce the cost of the system. Another main finding is maintaining a similar performance at scalable PEC systems. Such short-term scalable demonstration will lead toward practical application of PEC technology for green H2 production in outdoor conditions.
We also plan to further improvements in efficiency and stability of the PEC system by integrating photoelectrodes, e.g., photoanode-photocathode together, selecting a more efficient and durable catalyst.