Why does CO2 accept electrons?
Consider that the carbon in carbon dioxide is bonded to two electronegative oxygen atoms. This will cause shift the electrons towards the oxygens and away from the carbon, making it electron deficient:

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This makes the central carbon electrophilic, and explains the reactivity of the carbonyl moiety towards nucleophiles. Similarly, $\ce{CO2}$ undergoes addition reactions with Grignard reagents to form carboxylate anions.

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