Isolated Lewis Acid Site Enables Electrocatalytic Chlorine Evolution at Low-concentration Chloride Electrolyte.

Active chlorine production in concentrated brine is the most mature industrial electrolysis reaction. However, the chlorine evolution reaction (CER) suffers from poor selectivity due to the competing oxygen evolution reaction (OER), particularly in low-concentration chloride and high pH electrolyte. Here, an isolated site engineering strategy is proposed to improve CER selectivity by introducing a hard acid (HA) site to capture OER intermediates (OH*), thereby suppressing their competition with chloride adsorption at CER active sites. A silicon (Si)-doped PtRu catalyst was engineered via discontinuous, spatially separated incorporation, providing isolated Si sites that modulate the local coordination environment. Operando characterizations reveal that Si preferentially binds OER intermediates (OH*), while PtRu binds CER intermediates (Cl*). Electrochemical tests confirm that isolated Si sites suppress oxygenated intermediates (OH*) accumulation on PtRu active sites. Compared with PtRu, PtRuSi shows an enhanced Cl* desorption peak and a reduced OH* desorption peak during CER, along with a weaker methanol probe response in 0.5 M sulfuric acid during methanol oxidation reaction (MOR). Furthermore, the incorporation of Si modulates the catalyst interface, promoting efficient transfer of intermediates from OCl* to Cl*, thereby enhancing CER selectivity. Unlike conventional CER catalysts that are used in acidic electrolytes with highly concentrated sodium chloride (NaCl) (4-6 M), PtRuSi achieved nearly 100% CER selectivity in a low-concentration chloride electrolyte (1.5 M NaCl) under room temperature. Notably, PtRuSi delivered an average CER selectivity of 69.1% in natural seawater (pH 8.2), which was twice that of its PtRu counterpart.