You might just want to write about your work, but I recommend backing up a bit and writing some preliminary thoughts. What is your story? How did you get interested in this work? What excited you when you were a child or early in your school years? What was difficult for you to understand, and how did you figure it out?
If you want to get other people interested in your work, you need to express your own enthusiasm for it, but if you are an advanced graduate student (that is, narrowly focused, thinly stretched, over-directed, or just tired) then perhaps you’ve lost your way. You might have let your initial excitement about science or your particular field drown in the details of everyday life. You might even have become cynical.
Writing about your memories is good practice for many things: detailed sensory description, communicating with a lay-audience (outside your field), thinking about your own field from a different perspective, remembering what you used to think when you were outside your field, etc. It will also remind you of your early values and goals and dreams and excitement.
If you are interested in what inspired other scientists, then you might read Curious Minds: How a Child Becomes a Scientist, edited by John Brockman.
And if you are having real trouble feeling connected to your work, perhaps because your lab is full of people who seem to have forgotten their initial enthusiasms, start asking questions. How did they get into the field? What was their education like? What was exciting to them? What did they most love about engineering or science when they were 10 or 15 or 20 years old? These memories can bring you together, re-motivate more than just you, and also help you start to remember what it was like NOT to know what you now know. Remembering that will help you be a better teacher and communicator to an audience with varying levels of expertise.