Recent Advances towards the Development of an Aqueous Direct Solar Battery*

Energy supply by fossil fuels only has a limited lifetime and is responsible for an increasing environmental pollution, influencing also climate change. A rapid transition to more sustainable solutions is thus also in the focus of modern research. Renewable fuels are meant to circumvent supply fluctuations arising from energy sources like PV and wind, at the cost of infrastructural adaptations. Direct renewable energy storage is thus highly desirable, but expansive and complicated.
Herein, we report an earth-abundant polymeric material, which for the first time enables the synergistic coupling of two key functions of energy conversion within one single material: visible light harvesting and electrochemical energy storage. The “solar battery” anode material, a 2D cyanamide-functionalized polyheptazine imide (NCN-PHI), is the first of its kind being capable of storing large amounts of photogenerated electrons, operating even in aqueous conditions. Charge compensation and stabilization is realized by pseudocapacitive effects enabled by various aqueous alkali metal ions. Energetically, this occurs at energies well above the reversible hydrogen electrode, allowing for stable aqueous batteries with increased cell voltages.
Limitations arise from low conductivity and hole shuttling to a suitable cathode material. We herein present approaches that address these issues and present our work on hybrid material solutions for full aqueous solar batteries.
As such, we aim to provide a sustainable and cheap, earth abundant solution to overcome the intermittency of solar irradiation and other renewable electrical energy sources at a time.
Further information can be found in: “Toward an Aqueous Solar Battery: Direct Electrochemical Storage of Solar Energy in Carbon Nitrides”, F. Podjaski et al., Adv. Mater. 2018, 1705477.