Designing an electrochemical energy storage device using recycled Ti3C2Tx MXene and reduced graphene oxide spent wastewater adsorbents

• Direct upcycling of hazardous adsorbents into energy storage materials • Recycled rGO and Ti₃C₂Tₓ MXene as electrodes after heavy metal adsorption • Redox activity enhances electrode capacity by up to 50% over pristine materials • Full cells built from metal-loaded adsorbents show tunable voltage plateaus • Complex wastewater with mixed metals leads to additive electrochemical response This study presents an end-to-end approach for recycling hazardous waste heavy-metal-loaded adsorbents into electrode materials for electrochemical energy storage. Using reduced graphene oxide (rGO) and Ti₃C₂Tₓ Mxene as adsorbents for Hg²⁺, Cu²⁺, and Pb²⁺ from model wastewater solutions, we demonstrate their successful transformation into redox-active electrodes without any additional treatment. The recycled electrodes present superior capacity as compared to their pristine counterparts, while introducing distinct reversible redox features. Ultimately, the different recycled materials were assembled in full cell configurations, combining different metal-loaded adsorbents, yielding synergistic redox plateaus and an up to 50% enhancement in the initial energy storage capacity, depending on the metal pair and electrolyte used. The versatility of this recycling strategy was demonstrated across three aqueous electrolytes, including a water-in-salt electrolyte, revealing tunable redox behavior dependent on both metal and electrolyte characteristics. Furthermore, using a more complex model wastewater solution, containing two different metal cations, leads to a multi-contaminant adsorbent that exhibits additive electrochemical responses, thereby establishing proof-of-concept for the reuse of real-world wastewater adsorbents into energy storage devices.