Powershell script version of Sdelete -Z to zero free space on a disk.
Can be installed from PowerShell Gallery via Install-Module for Powershell 5.x and up.
Install-Module -Name Zero-Drive
Write Zero's to C drive with default settings
Invoke-ZeroDrive -Drive C
Write Zero's to E drive with blocksize of 1MB and leave 10GB of free space
Invoke-ZeroDrive -Drive E -BlockSize 1MB -SpaceToLeave 10