Rational Bottom-Up Engineering of Electrocatalysts by Atomic Layer Deposition: A Case Study of Fe_<i>x</i>Co_1–<i>x</i>S_<i>y</i>‑Based Catalysts for Electrochemical Hydrogen Evolution

A rational bottom-up engineering strategy for efficient electrocatalysts based on atomic layer deposition (ALD) is reported. The strategy involves compositional optimization of surface catalyst material by ALD for high specific activity and geometric optimization of electrode structure for high surface area. The two optimizations are decoupled herein, because the conformal ALD ensures that the coating of the catalyst does not depend on the substrate geometry. To demonstrate this strategy, we choose ternary Fe_<i>x</i>Co_1–<i>x</i>S_<i>y</i> compound as the catalyst for electrochemical hydrogen evolution reaction (HER). Compositional optimization shows that Fe_0.54Co_0.46S_0.92 is the best composition for high specific HER activity, and it is therefore chosen to be conformally coated by ALD on a high-surface-area CNTs/CC (carbon nanotubes on carbon cloth) electrode. The synthesized Fe_0.54Co_0.46S_0.92/CNTs/CC electrode exhibits a fairly low HER overpotential of −70 mV for achieving −10 mA/cm² in current density in alkaline solution, which demonstrates the effectiveness of this ALD-based engineering strategy