The paper announces a survey of a variety of devices and principles; when combined into hybrid realizations, the devices and principles claim to enable self-powered systems. The categories of devices and principles taken into consideration are solar cells, electrochemical cells, piezoelectric/triboelectric/pyroelectric generators, and magnetoelectric cells. Ignored are a whole range of other devices and phenomena that are usually researched or deployed for self-powered systems, such as electromagnetic energy harvesting, ionic cells, biochemical energy, classical induction variants, and others. It would have been useful early in the paper to give the interval of energy supply rates and temporalities studied at device and hybridization levels, as obviously this would help narrow the scope of the review.

The hybridization concept is not novel; it has been widely studied in microelectronics and consumer electronics, as well as in connection with combinations of renewable energy sources inside smart grids to self power, for example, islands, boats, or networks. Some combinations of the selected energy sources are described in connection with a wide variety of applications, and the combinatorics are obviously plentiful.

The core of the paper seems to be much more on combining piezoelectric and triboelectric nanogenerators and magnetostriction, which is indeed interesting and should have been better reflected in the title and the introduction.

Section 2 attempts at providing a theory for a nanogenerator on the basis of Maxwell’s equations for the displacement current, with an emphasis on the piezoelectric effect and on the triboelectric effect (as well as combinations of these two), in relation to the charge density in dielectrics and the electrode electron density.

Section 3 includes a compilation of some developments on piezoelectric generators and triboelectric generators, respectively, as well as combinations of both when feasible, with related backgrounds in ultrasound excited solar cells and pressure biocells. Output performance measurements are reported from literature, as well as on current rectification in ZnO n-p nanowires or sheets. There are also brief reports on carbon fiber/ZnO/nylon garment fiber collecting 3D mechanical energy, harvesting energy from raindrops, and the triboelectric collection of energy from human breath. Magnetoelectric composites in coupled cantilevers are discussed as well.

The paper concludes with limitations linked to integration and 80 references, mostly from 2015 to 2017. Unfortunately, typographical errors and missing information affect understanding. Readers should have significant background in at least one type of nanogenerator in order to grasp the challenges and achievements reported on.