Highly Efficient and Stable Perovskite Photocathode for Hydrogen Generation in Acidic and Basic Conditions

In the pursuit of sustainable energy solutions, the direct conversion of solar energy into fuels, such as hydrogen, through photoelectrochemical systems (PEC), holds immense promise. Organo lead halide perovskites with their excellent optoelectronic properties and their reported record photovoltaic efficiencies are therefore being researched for integration in PEC. Particularly, their integration as photocathodes for the hydrogen evolution reaction (HER) is gaining attraction due to their impressive HER photocurrent density (~ -20 mA.cm^-2) and high onset potential (~ 1 V). However similar to photovoltaics, the limited stability of perovskites in PEC devices is a critical challenge. This is further amplified due to immersion in an aqueous medium which is required for the operation of the PEC devices for HER. Previous research work have primarily focused on enhancing the extrinsic stability of the perovskite layer through the implementation of moisture-resistant encapsulant layers like Ni, Field metal, conductive carbon paste, metal oxide, or Ti foil. However, little attention has been paid to addressing both the extrinsic and intrinsic stability of the perovskite film, which is crucial for prolonged device operation. Intrinsic stability, crucially linked to ion migration effects leading to perovskite degradation, complements extrinsic stability, which is governed by the degradation of the perovskite structure due to decomposition with water (in the case of PEC). Moreover, selecting a catalyst capable of exhibiting exceptional stability and performance in extreme pH conditions poses a further challenge. While the kinetics of HER are facile in acidic conditions, alkaline environments present a hurdle due to the sluggish water dissociation step. Therefore, there is need for a single catalyst that can exhibit excellent HER performance and stability in extreme pH conditions In this work, we have fabricated a highly efficient and stable perovskite-based photocathode which displays excellent HER performance with enhanced stability. To enhance both performance and internal stability, a polymer additive has been introduced into the perovskite thin film. The use of the polymer greatly improves the solar cell efficiency, the polymer-perovskite cells have an efficiency of ~ 15.3 %, while the pristine perovskite cells show an efficiency of ~ 12 %. Additionally, we have synthesized a bimetallic catalyst comprising Au, Pt, and Ni, characterized by low overpotential and Tafel slope values for HER in highly acidic and basic conditions. The polymer-conjugated photocathode with the bimetallic catalyst layer exhibits excellent HER performance both in acid and basic electrolyte and shows high photocurrent density (~-20 mA.cm^-2), high onset potential (~ 0.95 V), and a half-cell solar to hydrogen conversion efficiency (HC-STH) of 10.11 %. More impressively, the photocathode exhibits an unprecedented stability, with T₈₀ (time for 80% degradation) values of approximately 70 hrs. (H₂SO₄) and 78 hrs. (KOH), retaining over 50 % of its initial photocurrent after 120 hrs. of operation. These stability values are the highest reported among various perovskite-based photocathodes.