The study reports a novel approach to enhance the alkaline hydrogen evolution reaction (HER) by combining highly oxophilic cerium (Ce) single atoms with fully-exposed ruthenium (Ru) nanoclusters on a nitrogen-functionalized carbon support. This combination effectively reverses the active sites from less active Ru single atoms to more active Ru nanoclusters, significantly improving the hydrogen evolution activity. The strong oxophilicity of Ce promotes the bonding of OH groups with Ce single atoms, while H atoms are preferentially adsorbed on the Ru nanoclusters, leading to a more efficient hydrogen evolution process. The Ce1-Ru_n/NC catalyst exhibits a mass activity of up to 10.1 A mg\(^{-1}\) at -0.05 V, outperforming most reported Ru-based alkaline HER catalysts. The enhanced performance is attributed to the synergistic effects between Ce and Ru, which promote water dissociation and hydrogen evolution. The findings provide new insights into designing highly effective alkaline HER catalysts by rational regulation of active sites.The study reports a novel approach to enhance the alkaline hydrogen evolution reaction (HER) by combining highly oxophilic cerium (Ce) single atoms with fully-exposed ruthenium (Ru) nanoclusters on a nitrogen-functionalized carbon support. This combination effectively reverses the active sites from less active Ru single atoms to more active Ru nanoclusters, significantly improving the hydrogen evolution activity. The strong oxophilicity of Ce promotes the bonding of OH groups with Ce single atoms, while H atoms are preferentially adsorbed on the Ru nanoclusters, leading to a more efficient hydrogen evolution process. The Ce1-Ru_n/NC catalyst exhibits a mass activity of up to 10.1 A mg\(^{-1}\) at -0.05 V, outperforming most reported Ru-based alkaline HER catalysts. The enhanced performance is attributed to the synergistic effects between Ce and Ru, which promote water dissociation and hydrogen evolution. The findings provide new insights into designing highly effective alkaline HER catalysts by rational regulation of active sites.