When a GPIO pin is set to output mode, you can either drive it "high" (ie: VCC), or "low" (GND). They can not, however, drive a negative voltage (ie: -VCC). If you want to create a negative voltage, you'd need some external GPIO expander chip sourced off some negative voltage supply, or you'd need to create a negative voltage rail source via a buck-boost converter or similar to generate it from Vcc.
Fortunately for you, Arduino already has a pieze-electric buzzer library, and wiring it up is dead simple. The relevant GPIO pin is connected to the buzzer's positive terminal, and the buzzers negative terminal is grounded.