Although these plants are described as easily grown houseplants they can be sensitive to several issues. This does not look like a disease or insect issue. Do not spray unless you know what you are spraying for. 

Some reasons for the black foliage may be a combination of overwatering, low light, may need repotting, adjusting to new location, etc.  

In general peace lilies have very vigorous root systems and can be rootbound.  Knock it out of the container and make sure the rootball is not in one big ball and the roots are not wrapped in a spiral within the container. Also, make sure the roots are firm and white and not mushy and brown. Remove any dead roots and prune unhealthy foliage. If potbound, using clean, sharp scissors or a knife cut the root ball into sections, and repot. If you break apart all the sections you can go to the next size up container or split and go into a smaller container or containers.  Make sure the containers have holes for good drainage. Use a soilless mixture that contains peatmoss, perlite, and vermiculite for good drainage. https://extension.umd.edu/hgic/topics/pottingrepotting-indoor-plants

 Peace lilies like to be in medium light, so we recommend placing your plant where it can get good strong indirect light. Direct sunlight will burn the leaves. When you water, do so thoroughly until you see water drain out of the bottom of the pot, and then let the top two inches of soil dry out before watering again. The plants need little fertilizer and only when actively growing from spring to fall. Growth slows during the winter. 

These plants can be sensitive to fluoride or chlorine in tap water. If you notice brown tips, you may want to try watering with distilled water. 

Here is more information on peace lily https://hgic.clemson.edu/factsheet/peace-lily/

Marian