There are various products available that are perfectly suitable for outdoor use, the key is to make sure that whatever product you choose is capable of withstanding the fluctuating temperatures and elements it will be in.
Porcelain tile: This is one of our favorites. It is relatively inexpensive and allows for great design freedom. It's available in a wide variety of colors, sizes, and trims, and can provide an outstanding look. Porcelain tile is perfectly suitable for outdoors, yet beware, ceramic tile is not suitable for many outdoor situations, especially those with freezing temperatures.
Granite: This is another popular choice for your outdoor kitchen design. Granite is definitely a first class choice but can be a bit formal for many outdoor kitchens. In addition, granite is not recommended for direct sunlight because of its ability to retain heat, so keep that in mind depending on the location of your outdoor kitchen.
Concrete: Another very popular choice and very durable for outdoor kitchen use. Concrete countertops have sealers applied for water and stain resistance. Left in its natural state, unsealed, concrete is porous and will stain.
Flagstone: Flagstone countertops are great and generally require little maintenance beyond routine wiping off of excess water to prevent mold and removing debris. Please be aware that it is not recommended to seal flagstone outdoors. Topical sealers applied to stone, installed in full weather conditions, may actually enhance the stone’s susceptibility to staining and discoloration.