Modulation　of　the　surface　chemistry　of　air　electrodes　makes　it　possible　to　significantly　improve　the　electrocatalytic　performance　of　solid　oxide　cells　(SOCs).　Here,　the　surface　chemistry　of　BaGd0.8La0.2Co2O6−δ　(BGLC)　double　perovskite　is　modulated　by　treatment　in　an　acidic　citric　acid　solution.　The　treatment　leads　to　corrosion　on　the　surface　of　BGLC　particles,　and　the　effect　is　dependent　on　the　acidity　of　the　solution.　As　the　acidity　of　solution　is　low,　Ba　cations　are　selectively　dissolved　out　of　the　BGLC　surface,　while　as　the　acidity　increases,　the　corrosion　becomes　more　homogeneous.　The　Ba　surface　deficiency　remarkably　increases　the　concentration　of　surface　oxygen　vacancies　and　electrocatalytic　activity　of　BGLC.　To　avoid　the　loss　of　Ba-deficient　surface　during　the　conventional　high　temperature　sintering　process,　a　sintering-free　fabrication　route　is　utilized　to　directly　assemble　the　Ba-deficient　BGLC　powder　into　an　air　electrode.　A　single　cell　with　the　surface　Ba-deficient　BGLC　electrode　shows　a　peak　power　density　of　1.04　W　cm-2　at　750　°C　and　an　electrolysis　current　density　of　1.48　A　cm-2　at　1.3　V,　much　greater　than　0.64　W　cm-2　and　1.02　A　cm-2　of　the　cell　with　the　pristine　BGLC,　respectively.　This　work　provides　a　simple　and　effective　surface　chemistry　modulation　strategy　for　the　development　of　an　efficient　air　electrode　for　SOCs.　©　2024　American　Chemical　Society.