Upcycling electronic waste into ultrasmall au nanoparticles via integrating ultrasound-assisted au stripping with tetraoctylammonium bromide-mediated phase-separation for CO2 electroreduction

The upcycling of Au from vast and environmentally burdensome electronic-waste rich in valuable metals provides a sustainable pathway for precious metal utilization and hazardous substance management. Here, we present a strategy that integrates ultrasound-assisted stripping with tetraoctylammonium-bromide (TOA-Br) extraction to upcycle Au from waste gold-finger printed circuit boards (gf-PCBs) into ultrasmall Au nanocatalysts for electrocatalytic CO 2 reduction reaction (eCO 2 RR), thereby overcoming the complexity and secondary-pollution inherent in conventional hydrometallurgy. Specifically, in non-crushed gf-PCBs, the Au-layer is stripped as foil, primarily driven by ultrasound-enhanced contact and reactivity between the underlying non-precious metal-layers (Ni, Cu) and the leachate. Importantly, the Au-rich slags from gf-PCBs are upcycled into ultrasmall Au nanoparticles (TOA-Au(SH)/PCB, 0.5–3 nm) via TOA-Br capture of AuCl 4 − in H 2 O 2 -regulated leachates, achieving Au recovery exceeding 99 % with impurities below 1.06 %. Mechanistic analyses reveal that the superior Au-separation efficiency arises from the H 2 O 2 -induced weakening of the coordination ability of active Cl − species toward metal ions in the leachate, while Au 3+ forms the strongly coordinated AuCl 4 − complex, which exhibits much stronger affinity for the electrophilic N atoms in TOA-Br than other metal-chloride anions. Moreover, the TOA-Au(SH)/PCB with abundant low-coordination sites achieves 94.59 % FE CO at −0.87 V vs RHE in eCO 2 RR, matching pure metal-salt catalysts (TOA-Au(SH)/pure, 96.97 %) and confirming gf-PCBs as effective Au precursors. We also find that trace Cu residues in TOA-Au(SH)/PCB promote eCO 2 RR activity, but precise regulation of Cu is required to optimize adsorption of key intermediates.