Direction of momentum given by the de Broglie relation
where is the mass of an electron, and is its velocity. In this case, since is a vector, it's clear that the momentum will be also a vector.
However if the momentum is a vector quantity (and it is), what is the direction of the electron's momentum given by the de Broglie relation
if the Planck constant is scalar and the wavelength is also scalar. Similarly the reduced Planck constant is scalar and the wavenumber is also scalar.