When I enter the command
Start-Process powershell -WorkingDirectory \"D:\\folder\"
it opens new PowerShell window with D:\\folder
D:\\folder
I also had the same problem and solved it with this command:
Start-Process powershell.exe -verb runAs -ArgumentList '-NoExit', '-Command', 'cd D:\folder'
Once you run the above command, Windows will launch with admin authority and the specified directory.