NOVELTY - Producing (P1) at least one nanofiber involves electrospinning fluid stock, where the fluid stock comprises metal precursor and polymer, and the weight-to-weight ratio of the precursor to polymer is at least 1:2; the fluid stock is aqueous; and/or the precursor is present in the fluid stock in a concentration of at least 200 mM.    USE - For producing at least one nanofiber; as electrospun nanofiber; as several nanofibers; as an aqueous fluid composition; and in sensor, battery, fuel cell, solar cell, ultracapacitor, catalyst, membrane, or electrode (claimed).    ADVANTAGE - The nanofibers have an average fracture toughness of at least 1.8 or at least 3.5 MPa.m1/2; have log(S/m) to log(S/m) ratio with an identical bulk material of at least 0.9; have an average length of at least 1 microns; have an average diameter of 1000 nm or less; have an average aspect ratio of at least 5 or at least 1000; have high quality and high performance; are highly coherent, long and tunable length; and have few voids and/or defects.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) an electrospun nanofiber (F1) comprising metal precursor and polymer, where the metal precursor and polymer is present in a weight-to-weight ratio of at least 1:2 (e.g. at least 1:1);    (2) several nanofibers (F2) comprising metal, metal oxide, and/or ceramic, and the nanofibers are at least 1 ~mm long on average, the nanofibers have an average aspect ratio of at least 5, and/or the nanofibers have an average specific surface area of 1-1000 m2/g; and    (3) an aqueous fluid composition comprising (a1) a polymer, and (b1) a metal precursor; the fluid composition is (i) a solution, (ii) a composition comprising uniform dispersion of metal precursor, or (c1) a composition comprising homogeneous dispersion of metal precursor; and (1) the weight to weight ratio of the precursor to polymer is at least 1:2 (e.g. at least 1:1), or (2) the concentration of precursor is at least 200 mM (e.g. at least 250 mM).    DESCRIPTION OF DRAWING(S) - Figure illustrates a schematic of the process and system of the disclosure.