Mitigating effects of heavy metal ions in wastewater with enhanced stability in hydrogen generation

For sustainable green hydrogen production, it is crucial to prioritize water-energy nexus, especially in water-scarce regions where it is challenging to deploy distilled water for electrolysis. We herein utilized heavy metal wastewater (HMWW) for H₂ generation (HER) but by first eliminating the heavy metal ions using membrane distillation (MD). As HM ions significantly interfere in HER (especially Cu), it is mandatory to utilize techniques such as MD that offer high rejection rate with low energy consumption to provide high quality treated water. The MD-treated water (permeate) was then explored as a water source in electrolyte with Pt/C as commercial HER electrode displayed a 14% decrease in HER overpotential with a 5 Ω decrease in charge transfer resistance in comparison to untreated wastewater (HMWW-feed). The initial studies indicated superior HER performance of permeate over HMWW-feed, probing comprehensive long-term HER electrochemical investigation to observe the prolonged impact of HM ions. From our observations amongst other HM ions in feed, particularly the exposure of Copper (Cu) ions, leading to electrodeposition on Pt/C electrode significantly deteriorated the electrochemical performance. The continuous exposure and electrodeposition of Cu on the Pt/C electrode declined the electrochemical active surface area (ECSA) by 75% in 72 h, leading to a 97% drop in the electrochemical stability of HER activity. On using MD-treated water (permeate), the electrode achieved a stability of 78%, approaching the HER performance of DI water as a water source (98.4%) post 72 h. The impact of HM ions was also reflected in the Faradic efficiency values for H₂ evolution that improved by 26% on using treated wastewater (permeate) instead of HMWW-feed. Therefore, leveraging MD-treated wastewater as a water source can facilitate the emergence of new sustainable solutions for H₂ generation with a low water footprint.