How to set a single axes' projection with cartopy.crs when using plt.subplot_mosaic

I am using the method ‘subplot_mosaic’ to create multiple axes, but I want to set one of the axes to be a GeoAxes with a specific geographic coordinate system. this method provides a keyword parameter called subplot_kw, but I doubt that it is called to set all axeses, not the one I selected.

gs_kw = dict(width_ratios=self.wratio, height_ratios=self.hratio)
        fig, ax_list = plt.subplot_mosaic(self.grids,
                                          gridspec_kw=gs_kw,
                                          figsize=(10, 8),
                                          constrained_layout=True)