PACS numbers:Black hole, a strange object of extreme gravity, is gradually believed to be a thermodynamic system after 1972. The area and the surface gravity of black hole event horizon were found to be closely related with the entropy and Hawking temperature. Then four thermodynamic laws were established [1]. Black hole phase transition as a characteristic nature and microstructure indicator has attracted a lot of attention.An isolated Schwarzschild black hole has negative heat capacity, thus it cannot exist stably. When the charge or angular momentum is considered, a branch of stable large black holes with positive heat capacity will emerge and they can exist stably. Hawking and Page found that there is a phase transition between large black hole and thermal radiation in an AdS space with a negative cosmological constant [2]. Motivated by the AdS/CFT [3], this Hawking-Page phase transition was interpreted as the confinement/deconfinement phase transition in gauge theory.Although there are different kinds of phase transitions, one remarkable difference between a black hole system and an ordinary thermodynamic system is that no pressure term exists for the black hole. A significant step toward this issue was shown in [4], where the cosmological constant is interpreted as the thermodynamic pressure. Then an AdS black hole system is more like an ordinary thermodynamic system. The corresponding conjugate quantity is the thermodynamic volume, which was found to equal to the geometric volume. However, they have different meanings, and this property are not required to hold for every black hole. Such phase space with the pressure and volume being included is now generally referred to extended phase space.Recently, the P -V criticality for charged AdS black holes was studied [5]. The results display that a first-order phase transition can occur among the stable small and large black holes at low temperature. At a certain temperature, this phase transition becomes a second-order one, which corresponds to the critical point. At this special point, the critical exponents and scaling laws were calculated. Moreover, they share the same values and forms as that of the van der Waals (VdW) fluid. Therefore, the precise analogy of the phase transition between the AdS black hole and the VdW fluid was established. Subsequently, this study was extended to other black holes, and it is known that the subject is Black Hole Chemistry.Besides the VdW-like phase transition, more interesting phase transitions were found. For example, six-dimensional single spinning Kerr-AdS black hole admits a reentrant phase transition [6] and multi-spinning Kerr-AdS black hole has a triple point [7]. We observed the similar triple point in Gauss-Bonnet gravity, and developed a novel way to shrink the parameter range where the triple point exists by counting the number of the extremal point of the isotherm.Comparing with the VdW fluid, black hole thermodynamics has two main differences: i) The relation between the black hole thermodynamic volume and spec...