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Caption : fig. s1：the optical pictures of unmodified chip (a), and teiep (b).

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Caption : fig. s2: (a) particle size distributions of pt. (b) pore size distributions of npg.

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Caption : fig. s3：sem images of au-sn alloy layer (a), and ag-sn alloy layer (b).

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Caption : fig. s4：low-magnification sem images of au-sn alloy (a) and npg (b); edx mapping images of (c) au, (d) sn elements corresponding to au-sn alloy, and (e) au element corresponding to npg.

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Caption : fig. s5: (a) eds images of ag-sn and ag/agcl, and the insets show the composition respectively. (b) xrd patterns of ag/agcl.

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Caption : fig. s6: sem image of commercial ag/agcl pastes with different magnification.

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Caption : fig. s7: (a) linear polarization curve of planar ag/agcl and porous ag/agcl in 0.1 m pbs containing 0.01 m kcl. (b) open circuit potential (ocp) test between porous ag/agcl electrode and a commercial ag/agcl (3 m kcl) reference electrode in 0.1 m pbs containing 0.01 m kcl.