Scalable microfluidic synthesis of noble metal single-atom catalysts.

Scalable synthesis of noble metal single-atom catalysts (SACs) is crucial for practical applications but remains challenging due to the 'scaling-up effect' by spatiotemporal variations of concentration/temperature, leading to poor uniformity and/or metal aggregation. Here, we report a continuous-flow microfluidic strategy for mass production of Pt SACs on hierarchical nitrogen-doped carbon nanocages (Pt1/hNCNC), which fundamentally overcomes this limitation. Combined experiments and theoretical simulations indicate that the microfluidic microreactor efficiently avoids local supersaturation via rapid and uniform mixing. In synergy with micropore trapping and nitrogen anchoring of hNCNC, continuous local adsorption equilibrium is maintained, promoting stable immobilization of isolated atoms while suppressing aggregation. This method achieves scalable synthesis of Pt1/hNCNC SACs with high Pt loading (10 wt%), excellent uniformity, and a nearly 300-fold increase in productivity compared to the batch method. When applied in a proton exchange membrane water electrolyzer, the cathode with an ultralow loading of 20 μgPt cm-2 delivers industrial current densities of 1.0/3.0 A cm-2 at low voltages of 1.66/2.00 V, respectively, and operates stably for over 500 h at 1.0 A cm-2. This microfluidic synthesis is also successfully extended to various noble metals (Pd, Au, Ir, Rh, Ru, and multi-elements) and nitrogen-doped carbons, demonstrating broad generality. This work establishes a practical and scalable paradigm for manufacturing high-performance noble metal SACs with deep insights into the dual-scale cooperation between macroscopic fluid dynamics and microscopic support chemistry, bridging laboratory discovery with industrial application of single-atom catalysis.