  For any 0-cell $B$ in a 2-category $\Bc$ we introduce the notion of adjoint
algebra $\adj_B$. This is an algebra in the center of $\Bc$. We prove that, if
$\ca$ is a finite tensor category, this notion applied to the 2-category of
$\ca$-module categories, coincides with the one introduced by Shimizu [Further
results on the structure of (Co)ends in fintite tensor categories}, Appl.
Categor. Struct. (2019). https://doi.org/10.1007/s10485-019-09577-7]. As a
consequence of this general approach, we obtain new results on the adjoint
algebra for tensor categories.
