The general purpose of these designs are described in “3D Printed UV-vis Cuvette Adapter for Low Cost and Versatile Spectroscopic Experiments”, which is published in the open access journal ACS Omega. Link to publication:
http://pubs.acs.org/doi/abs/10.1021/acsomega.7b01310

This particular part is meant to enable spectroelectrochemical experiments. In this design, we have a path length of 10 mm and is meant to hold a planar and transparent working electrode like ITO or FTO. A reference electrode can be placed in the adjacent hole and the counter electrode placed in the second hole. Note that the counter electrode hole is connected to the main electrolyte compartment via a tunnel running underneath. This adapter can be used in most standard UV-Vis spectrometers. We recommend printing this design with a black filament to reduce the amount of light scattering.

An instructional video to assemble the spectrometer is shown below with the materials used listed. Either quartz or glass windows can be used depending on the spectral range needed for the adapter.