See PCF8574 datasheet. A high output is through pull-up resistor. It's one of the key differences with the (slightly more expensive) MCP23008 and MCP23017.
An ESP01 has VERY few pins available, you should be able to remap I2C pins to GPIO0 and GPIO2 but it feels very much like a hack to me. Use a NodeMCU or WeMOS D1 Mini instead, then you have all pins of the ESP8266 broken out. Those boards are much easier to work with.