( This ( ( was ( ( a ( standard format ) ) ( ( for which ) ( ( such cells ) ( were ( ( exploited ( for ( spontaneous ( chemical reactions ) ) ) ) ( to ( generate ( electrical energy ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT This)) (VP (VBD was) (NP (NP (DT a) (JJ standard) (NN format)) (SBAR (WHPP (IN for) (WHNP (WDT which))) (S (NP (JJ such) (NNS cells)) (VP (VBD were) (VP (VBN exploited) (PP (IN for) (NP (JJ spontaneous) (NN chemical) (NNS reactions))) (S (VP (TO to) (VP (VB generate) (NP (JJ electrical) (NN energy))))))))))) (. .)))
This was a standard format for  which such cells were exploited for spontaneous chemical reactions to generate electrical energy.
(ROOT (S (NP (DT A) (JJ voltaic) (NN cell)) (VP (VBZ generates) (NP (DT an) (JJ electric) (NN current)) (PP (IN through) (NP (NP (DT a) (NN reaction)) (VP (VBN known) (PP (IN as) (NP (DT a) (PRN (-LRB- -LRB-) (NP (NN n)) (-RRB- -RRB-)) (JJ spontaneous) (NN redox))))))) (. .)))